Thanks for A2A. This is a very good question. In fact so good that I feel kind of inadequate trying to answer it. But will try my best depending upon what I have seen and my personal thoughts on the subject.
Often being debilitated, a planet is unhappy and uneasy, as it is placed in a situation that is UNNATURAL and OPPOSTIE for its nature and principle. So it acts something else while it is something totally different.
E.g. an exalted mars would make one a warrior whereas a debilitated mars would make him boil inside with impotent rage. An exalted Sun behaves with reckless abandon and a sense of entitlement, debilitated Sun would work its ego inwards, making a person often behave like a snob while doubting if he is actually worthy. An exalted moon keeps its calm under all circumstances whereas a debilitated moon would act very cold outside while dealing with emotional havoc inside.
Similarly, Venus is a planet of love and mysticism, being pushed into the super practical non-romanitc sign of Virgo, loses its creative and mystical liberties and becomes hemmed in the confines of uber-pratical earthy servant sign. It longs to be free and express its creativity but it is force to stick to the rules. It is like putting an artist in accounting department. You get the picture.
My personal theory is that just like all lessons in astrology this comes as a KARMA. Or may be, just may be, you overused something, or were proud of it or even abused it. May be the one who used to have an exalted mars was a bully in last birth, this birth it is his turn to feel impotent anger. The emotionally stable person who manipulated others and caused them tension gets a damaged moon in next life.
May be you were a beauty queen in last life with exalted Venus in Pisces making fun of lesser mortals for their dressing style, breaking hearts was a part time hobby and belittling others was a birth right. Karma, my dear, is a bitch.
So next life comes a debilitated Venus. So no matter how pretty you are, you would have doubts about your beauty and style and your worthyness to other gender. Good news is that a Virgo Venus often comes with a Neech Bhanga raja yoga as Mercury is often sitting with it in Virgo which is Mercury’s exaltation sign. This not only cancels most of the bad effects of debilitation giving a certain clumsy beauty back, but then you would have amazing smarts and a strong luck.
Not bad going from dumb supermodel in one birth to cute geek in the next one. I would rather have this debilitation than most others. 🙂