There are a B+W Clear filter on all of my lenses just for protection. That means I spend a lot of money in filters and I have saved even more in lenses.

It's all depends of the work you have to do. In my case lenses are in danger very often. Even when there are no risk of being damaged but it's raining or I'm in a dusty place, I keep the filter because I prefer to clean it instead of the lens.

I don't know how a clear filter affects to the image but I can assure you that no one of my customers have ever said "I don't want this pictures: they are taken with a filter".