Emphasis on the slightly. Making 30ish mm rims will minimally improve the aerodynamics on your bike, and are usually heavier, which I find less desirable in a rim. Contrary to what AEO says, you WILL probably notice the rotational weight difference between an aero wheelset and lets say open pros, while you would be unlikely to notice any difference in ride quality from the profile. The added weight does make the rim stronger, but unless you are planning on doing hipster tricks or weight over around 300lb, I personally think that the difference in strength is also negligible. Dont get me wrong, CXP33s are nice but it boils down to a smal difference in weight (I personally would rather have sightly lighter, more nimble open pros) and the question of aesthetics.