Does the plastic cap on a Presta valve serve any purpose once fitted to a rim? I can see the use of the valve cap on a Presta valve when the tube is still packaged (it obviously stops the valve puncturing the tube), but does it do anything except look pretty (or not) once you've fitted the tube to a rim?

I've kept them on out of habit, because I've had problems with sticking Schrader valves in the past when I've lost the caps and dirt/grime has got in there - but the design of Presta valves suggests to me that they wouldn't suffer this fate.

Given that I really need to inflate tyres on a road bike every day, is replacing this cap something I can leave out of my daily chores?
The cap keeps dirt and rocks away from the valve, particularly the fragile release mechanism. It's not the end of the world if the caps are missing, but I suggest leaving them on. They don't take that long to remove and replace.