(1) Regardless of ascendant or Moon Sign – all Mahadasha mean something which is THE SAME for all people! For example, Surya (Sun) mahadasha is about creating your own presence, your own product, skills, your own identify, your own presence and brilliance, it also means Govt, Father and Seniors at workplace, police etc authority related karma – This is regardless of ascendant or Moon Sign. Chandra (Moon) mahadasha for all people it is about: people contact, getting things done thru people but not masses -- more of classes, colleagues, Mother, Women, sharing sentiments etc and building collaborations and so on. The products or skills acquired in the Surya Mahadasha spread to a larger geographical area in Chandra Mahadasha. Rahu is about paternal family history events, but also about aggression and hedonism, image, insatiable desires and so on. Rahu also means people of different caste culture & religion or language. So, this is like 60% importance for a Mahadasha which is regardless of ascendant or moon sign.
(2) Regardless of ascendant or Moon Sign – If a planet is well-placed --- which shows Kaarmic Reward – i.e. unpaid karma from the past life or your karma that flourished quite a bit after you were gone or you could not enjoy. If the planet is “badly placed” then it means Kaarmic Burden / Debt that to be paid by good deeds or sufferings or combination of both.
(3) Regardless of how GOOD or BAD a planet is placed, its mahadasha would affect the house which is next to it adversely in a way --- or the house that is 6th from it or 8th from it --- as any planets does impact adversely the houses that it is 12th 6th or 8th…! Example: A planet in the 3rd house well placed – good for speech, expression, TRAVEL and art etc BUT doesn’t allow to enjoy the HOUSE/HOME much!
(4) Obviously now – Ascendant and Moon would show subjects or areas of your presence where these Mahadasha would play out! i.e. ascendant and moon sign would show the TOPIC or area of life or career etc and how that would play out depends on the planet. For example, Vrishchik shows power games, politics or chemisgtry, chemicals or audit, policing, military and so on. Yes, Mahadasha of owner of the houses like 1 5 9 10 11 tend to be more significant for “common people” – but for an artist 3 5 owner are very imp – for a Yogi – 4 8 12 owners would be more beneficial. For a Doctor – L6 Mahadasha would be VERY VERY imp!!
(5) A well-placed planet Mahadasha regardless whether it is in the 6 8 12 houses would show significant gains – where it is placed --- which houses it owns and whether it is friend of Ascendant owner of Moon sign – it matters to an extent. Also, Ascendant or Moon Sign ---- would show how significant would be the mahadasha.
(6) For example Jupiter (GURU) mahadasha which shows education, professors or teachers, knowledge and KIDS for a person --- it would be more significant for Jupiter ascendants, Mercury ascendants as both ascendants show education, learning, teaching etc. Jupiter also shows direction, thought leadership and guiding others – so it is highly significant for Sagittarius, Pisces ascendants and Virgo. Gemini ascendants. Aries and Scorpio, it IS important but given other planets are well placed.
(7) Jupiter mahadasha brings you (if well placed) in connection with good guides, philosophers, Gurus, Sages and good thought leaders and you get great advice – “Sunt-Samagam” is what a well-placed Jupiter shows. Proximity to great thoughts, thought leaders, mentors, Gurus, Sadhus and so on. It also shows gaining some secret or patented knowledge. Raj Thackeray in Jupiter mahadasha (10th house Jupiter, Scorpio Ascendant and Capricorn moon sign) was always with his uncle (THE Balasaheb!!) and had connections with ShivShahir Purandare and rather experts of all sorts of fields from 1993 to 2009! For him Jupiter is owner of 5th house Buddhi and investments (2nd).
(8) Jupiter being exalted in Kirk and say in the 2nd house which is economic zone and that too 7th to Moon which means very good thoughts (sensing ability, imagination, logic so on). Jupiter Maha would show great economic progress, investments, family doing good – Kids doing good. Great advice from experts in all fields, saints, mentors Guru and more so on Economic matters!
So hope this answers Generic question on Mahadasha.
 Another Topic ------- AstroQuick: even if you are the most selfish man out there, you have got to be highly selfless to achieve your selfish motives and objectives! The more you help others and make them successful the more they help you in turn to achieve unimaginable heights. A guy who ran an IT company successfully but ran it for limited motives and sold it in 2011 etc earned a lot lesser than the man who ran it by sharing his wealth and empowering people (Murthy). So he earned multiple times more by being selfless! :)
Salman holds his pants and belt and does a zataka and people throw money at him..... If we did that we would get stones...:): it's the daan-dharma that he has done and money wealth he gave away in past birth to people is being thrown at him by people now in his Shani mahadasha.
So if you are selfish you are lot better served by sakaam karma than say nishkaam karma. As Brian admas also says "if u wanna be bad, you gonna be good" (or something very similar -- don't remember exactly) :)
 End of Raahu Mahadasha if well-placed
END OF RAHU MAHADASHA if very well placed in your horoscope is end of a mystical period: Like Sunil Gavaskar ending his Glorious Test Career and Dilip Kumar ending his charismatic 18 years as a super actor and super star!!
This mahadasha shows some un-quantifiable gains or sufferings or unfulfilled "glorious" pursuits. The results of this mahadasha are directly proportional to the unpaid karma (both good bad) of your paternal grandfather and his siblings or his family folks. More so grandfather/mother himself. End of this mahadasha embarks GURU mahadasha which means -- insatiable desires and glorious pursuits give way to more Quantifiable efforts and projects in life. The projects that have VISIBLE effect on the world and has goodness to it and has WELL DIRECTED karma than Rahu's uncontrolled desires frustrations or agitation or highly material hedonist behavior ------ So it is good bad based on your paternal grandpa's life! :):) So Guru mahadasha brings in angle of mentoring, education, Kids and overall a well-directed life... like Gavaskar's commentary and his help to India cricket or BCCI --- etc etc. Last Antardasha of Rahu mahadasha is that of Mars which prepares you for Guru Maha.
Hope this helps!!