The first thing I can think of is that if you're writing a flood-filling algorithm (finding connected components) you should fill with #s instaed of Bs, even if filling with Bs is more conventional. Specially if you're doing competitive programming and need to overkill the optimization process in order to pass the run time.

As for production coding, I can't think of anything. Any ideas?

BTW, this is probably speculation, but it's still worth discussing in my humble opinion.