Well its never a "BAD" idea to get an alignment after steering/suspension has been r&r'd however ,I have replaced probably hundreds of wheel bearings and/or ball joints and no need for alignment. this isnt just from assuming either.Way back in the day(haha) we experimented with this at the shop I worked at. I think all in all we checked about 10 or so after such a repair and it was never out of spec (we also checked befor hand) and a couple of times it didnt even change at all. Of course we always mark things so we can put them back so I am sure that helps!
Of course it is important to remember a change in any one of the 3 major components of alignment(camber ,caster ,and toe) effects the othe two.
All of this is maybe too much info(sorry) but what I am saying is ...
It doesnt hurt to get an alignment ,but its not needed if done properly.