We've had related discussions twice:
The general consensus seems to be that any technique is fine as long as it's comfortable and doesn't have high potential for injuries and stuff like that. So, if it isn't hurting you, go ahead and use your pinky.
But it also seems to be the case that some schools discourage it (and some don't), perhaps not because of injuries, but because of some other reasons? In
hybrid picking some techniques you use it, but in classical training you mostly avoid it, or sometimes completely absolutely no flexibility possible prohibit its use, depending on the teacher.
This all is addressed in the questions linked above. The thing that is not addressed is why. Why some specific schools of finger-style see it as a negative, and discourage it, and even strictly prohibit it (not in a "fingering police" way, but in an "achieving the most optimal technique" way)?
Is it too slow? Is it too weak? Is it too inaccurate? That can be improved with practice, right? Is it too small? That can be minimized by compensating, like the curving of the fingers and adjusting the angles involved, right?
Same applies to all our other fingers (from both hands), so why is the pinky being singled out? We use the pinky of the fretting hand extensively, so why the discrepancy? What's the reason behind some schools of finger-style guitar avoiding the use of the pinky finger?
Some background examples:
In classical guitar music, we do occasionally use the little finger. Not often, but sometimes. And it’s more likely in advanced music. Using the right-hand little finger generally falls into the category of “special effects”, or special techniques.
"...in hybrid picking you use it, so no challenge here...": I don't. Most people I know don't. And I dare say most known guitarists I'm aware of don't. But perhaps I'm wrong. I'd say, but it's just a guess, that for most people thumb + index through ring finger comes most naturally. My pinky is too short (and too weak) to be of practical use, without contorting my hand in a very awkward and straining position. It simply seems to be what works for the vast majority of players, and therefore also what got taught. I use my pinky for artificial harmonics (but not always) but that's about it
In fingerstyle guitar, the picking-hand pinky is often not used at all.
I am a classical guitarist. Left hand pink - certainly (I'm sure you assumed that already)! Right hand pinky... almost never. Only exceptions are really in some forms of rasgueado
It seems that the C/pinky finger is not normally used for sounding strings, though it is certainly used on the fretting hand. Looking at YouTube clips of Julian Bream, you see that he never appears to use the smallest finger on his right hand. It is a little deceptive since the pinky remains tightly coupled to the ring finger and moves with it, in a kind of sympathetic reaction, though it does not contact the strings.
Every fingerstyle channel or resource I come across says to either use the pinky to rest above the soundhole to 'lock' the other fingers into place, or to just leave it floating about if it's not comfortable to do so. The only time I have heard it recommended is for flamenco.