I have never understood that logic. If you have a 250gallon/hr skimmer it will skim 250gallons in an hour regardless of how fast the water is going by the intake. (Just sayin)
I personnaly like a lot of flow through the sump because it keeps detritus off the bottom, aerates the water, and provides more flow in the tank where the returns are. It also gives my fans a lot of opportunity to cool more water before returning it to the tank.
Gas exchange is good (for pH and O2) and so is evaporation if you are trying to keep your tank cool in the summer.