How hot is hot?
Up to a point it is beneficial to have mesh or well ventilated clothing. Above some point in the low 90 degree range the ventilating air becomes a handicap, and you are better off sealing yourself from the outside air and doing something else to rid your self of excess heat.
Generally, that is the point when I quit riding, but if you live in the tropics or desert, or plan to ride through it, I guess that you learn to adapt to it (with cooling vests, etc.) the way that I have learned to adapt to the cold (with electrically heated gear).