What other option did we have?
When the Jazz decided not to give Boozer $80 million, they had a list of 8 or 10 PF prospects they were interested in. Al Jefferson was reportedly #2 on that list. I'm not sure who #1 was, but ostensibly one option would have been to offer a big long-term deal to David Lee. I actually liked the Big Al signing overall, and still do. The problem with the Jazz has mainly been backcourt play, outside shooting and the lack of other scoring options in the half court set. Al was entering his prime and was on a 3-year deal. It wasn't a bad move, imo. The Jazz saved $40 million on Boozer, moved Millsap into the starting line-up and kept a bit more flexibility. David Lee wouldn't have been able to play center next to Millsap and doesn't really defend better than Al does.
As much as people complain about Al, he still leads the team in scoring and rebounding, and the league still regards him as our "best" player.
Edit: After the DWill/Sloan fiasco, the Jazz have been holding Al as an asset while rebuilding. Al has helped Kanter develop and has helped keep the Jazz competitive.