Pape Sy is probably never going to be a useful NBA player. In that respect, the decision to waive him (along with Magnum Rolle and Brad Wanamaker) is perfectly defensible for a team struggling to reach the league's roster minimum without going over the luxury tax line.
It does not make the decision to draft Sy, despite his age and lack of professional experience, or to buy out his contract despite their being no role for him to play on the 2010-11 Hawks team any more explicable. The Hawks spent money on a player who wasn't ready and, after his first, brief period professional success, they give up on him.
Sy's tenure with the team demonstrates the same lack of long-term planning and wasteful spending as does the need to fill out the roster (again, minimally fill out the roster) with replacement level players in their thirties because of habitually poor cap management and player development, factors which are far more likely than Pape Sy's presence or absence to impact the 2011-12 Atlanta Hawks season negatively.