Like a few others, I've always stretched new strings after putting them on. Put them on, tune to standard, give them a good stretch, tune up again, stretch again, tune up again.
Is it beneficial?
Good question. I think it is beneficial, tuning stability is achieved almost immediately, great if you're on the road or in the studio. Does it effect your "tone"? I've never noticed any detrimental effects from doing it, so no.