Originally Posted by
joedab
Not sure if this applies in this case with the headset loose only to the point of feeling a bit play while holding the front brake and rocking the bike
That means your headset is too loose. Headset bearings should not have play.
Originally Posted by
andrewclaus
Maybe the LBS guy was talking about the fit of the cup into the frame, not the bearing adjustment.
The LBS guy was talking about bearing adjustment. If there's play in the bearings, then the impacts that headsets deal with all the time aren't being distributed nicely across the full race, they'll be hammering the front and back of the races. That's bad for both the bearings and the thing they're sitting in.