BPA generally seems to be the best idea, but there are a couple of exceptions:
First, if you already have a star PG and the BPA is a non-shooting, smaller PG. In this case, you are just screwing yourself before you even put your team on the floor by drafting a player who absolutely can't play with your current, very good PG.
Another is what happened with the Sixers. They picked three top of the draft centers three years in a row who can't shoot outside of five feet. In general, I am okay with picking top notch big guys, but at least one of them needs to be able to spread the floor.
As the draft moves well past the lottery, I am also okay with teams picking for need. There usually isn't a great of a distinction and perennial playoff teams generally need to find players to fill roles rather than finding the next big star...but good players do slide and teams should be willing to take a chance.