Never.
Character development is one of the pillars of an RPG. I always build my characters myself.
^This! I love character creation and planning the character, and - surprise, surprise - I love seeing that I made it suboptimal too. Actually, I want there to be heaps of ways I can "build" characters the "wrong" way. Min-maxing can be fun, but I leave that for later playthorughs. The first ones I usually go more all-in RPG-wise.
In short, I have never and will not ever use an auto-assign button, but I can easily accept that the option is there for other players.
