When CO first pulled half the F seats out of it, they said the 753 was for "leisure markets" such as Florida. However I've seen them on both leisure and business routes, arguably more on business routes than leisure routes:

Leisure:
IAH-FLL
FLL-EWR
IAH-MSY

Business:
EWR-IAH
IAH-LAX
LAX-EWR
IAH-SEA
SEA-ANC