As the post above mine mentioned, and as you've said, it can "hurt" financial and logistically when it comes to interview scheduling, having to write all the cover letters, etc.
However, beyond that, no--it doesn't hurt to apply to more sites. Although do keep in mind that while on interviews, some sites will ask either where else you applied, or where else you've gotten interviews. Just as in grad school, this is in part done to see if there's any coherence/link between sites in terms of interests, training, etc.
And regarding one of the above posts re: hours earned in a master's program, those go on the APPIC in a separate section devoted entirely to masters hours. They're definitely not counted in your doctoral program totals. However, don't let that confuse those of you who earned your master's en route to your Ph.D./Psy.D. (i.e., in the same program), as those hours do of course count in the standard APPIC doctoral program hours spots.