I used to play classical. My teacher never taught me to play with my pinky on my picking hand, thus i never did it. But I say use it if it feels to be comfortable thing for you. I don't agree with people that say, "never use this technique." I play with a pick now and i use economy picking, which is supposedly the wrong way to pick but i'm doing well with it. Classical can be very strict though, and i think that sometimes takes somehing away from the music.