If you care about your performance on the bike, then you should really take interest in the influence that the proper clothing has. 

For instance, a proper, close-fitting jersey can save you approximately 15 watts (riding alone at 45 km/h) compared to a “flapping” shirt. The advantage you get from the close-fitting one is about 2 seconds/km. 

If you wear a time-trial skinsuit, then the advantage you get is about 4”/km. For example, in Bordeaux, Tony Rominger - pedaling at 420 watts- rode at 51km/h when wearing a normal road jersey and could exceed 53 km/h when wearing a skinsuit. 

Clothing becomes even more important in extreme weather conditions, such as very hot and very cold environments: both hypothermia and hyperthermia can be fought with proper fabric and colors.