If I had a touring bike, they would stay on, without doubt.
But my single speed is too pretty for rain and the road bike looks like a tractor with them fitted (as they are)
Its all about the aesthetic for me!
Actually, winter rain, or rather winter wet roads are a pain. Thick with grime and grease, mud and salt.
Summer wet roads are not as messy and in may ways cleaner on your clothes (up your back).
Only a proper downpour in the summer leaves me wanting for guards...which is rare. Whereas every wet ride in the winter makes me glad I have them fitted.