I'm a jazz and rock guy--I don't have the chops to play orchestral in public.
That said, I think the benefit of any public performance is "tempering", or giving YOU the confidence to perform "under pressure." (That why music schools stress performance so much as a regular part of the curriculum).
Or better said, the more you perform in public, the less pressure you feel each time you do it.
Pro musicians often describe the benefit of practice as raising the FLOOR, not the CEILING, of their playing, so even their WORST performance on any given day is acceptable (to them and the audience).
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edit: in thinking about your post, I keep getting hung up on the word "validation", and I'm not sure how best to interpret it, and don't think I addressed it.
I've had some amazing (public) performances that I'll never forget, but some of the most memorable moments have also happened in rehearsal rooms.