I think of the Chromatic scale as just a way to add more sounds into a scale i'm already using. If I'm playing in the G Major Scale, and all of a sudden i want to build up for a climax, it makes alot of sense to do a chromatic run up the G scale to the next octave (and sounds nice, too). Playing the chromatic scale well is one of the most difficult things to do, because distinguishing between each semi-tone (and there are no whole-tones on the chromatic scale), it takes alot of 'touch'.

Alot of Jazzers were into chromatics, check out any random jazz player to find his scales filled with chromatics, as well as all the modes you can think of.

~Incidents