I was wondering myself!
I noticed when I hang with heavy weights I can’t even kegel properly, although if I stretch it SO with my hands as far/hard as I can, kegels might be a little difficult, but I do feel them.
I am not sure if it has much to do with gaining, maybe it has something to do with gains when it comes to jelqing/clamping/girth work, and it might impact length as well, you probably noticed kegelling kind of pulls the penis back, at least it looks like it does, so kegeling and stretching past that kegel pull while holding the kegel itself might be some sort of exercise…I hope you get some answers, I too wish for a good answer on this topic. Thanks!