What a weird thread title, what triggered this? Evan Turner is cheap short-term bench scoring, I think most C's fans know that, nothing wrong with this signing.
I think it was inspired in response to some perhaps overly-excited commenters comparing Turner to a 'poor man's Paul Pierce' and already installing him as the starting SF (insisting a Green trade was imminent and that Turner was better than Green anyway). Some Celtic fans' only knowledge of Turner was from his games against the Celtics - in which tended to play some of his best games.
As usual, attempts to impose a dose of reality on that enthusiasm just resulted in hyperbolic exchanges to either extreme: Turner is Great! Turner Sucks!
Financially, this is a low-risk deal. The only real significant risk is potentially locker room chemistry -- given Turner's reputation. But both Sullinger and Brad Stevens are apparently familiar with Turner from way back so perhaps that will mitigate that risk.