One scenario I can think of when you might do this is if you fall in love with a particular bike or brand of bike, and your LBS is just simply not a dealer of that brand. Doesn't mean you don't want them to stay in business if you buy the bike elsewhere but still use them for the fit and maintenance.

I, for example, just got it into my head that I wanted to ride a Blue RC4. It was a pretty superficial decision, but still, that was the bike I wanted. Nobody around here carries that brand at all...