Totally depends on the situation.
If you're drafting a player projected to be a franchise changer like Lebron or Durant, then the most rational decision would be to build around that player.
I think that in 2007 if Ainge ended up with the no 1 or 2 pick, he selects Durant, decides to build around him and some of the younger players were on the team at the time like Al Jefferson, Perkins, Delonte, Tony Allen and go from there. I don't think he makes the KG deal and I also think it's possible he would've dealt Pierce as well.
However, if you're drafting nothing but players that are projected to either be role players or fringe starters, then dealing for an all-star and convincing him this is the place to be is the way to go.
I think the same applies this summer, really.
If by some chance the Celts landed a top 3 pick, then odds are that DA keeps the pick and looks at either Embiid, Wiggins or Parker (whoever fell to him) as a major building block.
But, when you land the no 6 pick, you aren't going to find many players to build around (except maybe the 1979 draft when the Celts drafted a guy named Larry Bird. That is a very rare occurence.)