I'm a guitar player, and I studied classical guitar for a number of years. Flamenco players tend to use all four fingers. To most classical guitarists, this is considered taboo. I don't know that I ever heard a good reason for it other than it was the convention. So many classical methods (Tarrega for instance), are based in this style. Next comes the question of flesh versus nails, and we can consider Segovia's influence upon guitar in his incorporation of both. Who can say that one way, is the only way when such masters might have disagreed (if they had been able to meet). I learned the pima technique, and never felt a lack of fingers to cope with six strings. As of now, I play a great deal of music by hybrid picking (pick plus fingers). Like the others have said, do what works best for you. If you learn from a teacher, you may find it necessary to adapt to that style, and there are often benefits.
Your hands are like dogs, going to the same places they've been. You have to be careful when playing is no longer in the mind but in the fingers, going to happy places. You have to break them of their habits or you don't explore; you only play what is confident and pleasing. I'm learning to break those habits by playing instruments I know absolutely nothing about, like a bassoon or a waterphone. - Tom Waits
