" I only put it on if it's a situation where I think the filter will be beneficial."
Like keeping the front lens element clean! 
Plus some considerable protection from natural 'elements' like rain.
High quality protecto filters rarely cause disagreeable reflections. If it should, remove and replace it when done. Simple, no?
@TCampbell wrote:It isn't so much the actual "glass" that you need to worry about ... it's the coatings on the surface of the glass ... you don't want to use anything so harsh that it damages or removes those coatings.
And of course... you don't necessarily want to use something that leaves any residue behind.
A speck of dirt of dust on a lens wont show up in the image (the dust would have to be at a focus point in order to show up.) So I'm not so obsessed about grabbing a cleaning cloth every 10 seconds if I see a spec of dust (if you can't see with your eyes from a few feet away... then it probably doesn't need to be cleaned.)
UV filters are redudant (there's a UV filter inside your camera) -- but are sometimes used to protect the lens from dirt or smudges (or sometimes "clear" filters). These are, of course, optional. But keep in mind that even these may have anti-reflective coatings (the good ones do). If it doesn't have anti-reflective coatings, that flat "glass" filter can create reflections or 'ghosting' in your image. Even filters that do have coatings will have ghosting ... but usually just require brighter points of light before the problem shows up. The main point is ... in some circumstances the filter will degrade the quality of your image. So while I "own" filters that can attach to any of my lenses, I generally don't leave them on the lens all the time. I only put it on if it's a situation where I think the filter will be beneficial.
We are going down the much-travelled path of when and how to use filters as protection. Like anything else there is a cost (both financial and performace)/benefit relationship here, thus to quite a degree it depends on how you use your cameras. If, for examply you did most of your photography under controlled conditions then a filter may be rarely or not used at all. On the other hand if there is a greater risk of damage to the front element by being used in challenging conditions, then a filter is a much cheaper solution to having the front element of a likely expensive lens replaced. Actually, I don't know of any lens repair that could be considered cheap... 
In terms of being knocked or dropped it is often suggested that a lens hood will provide protection and there is certainly an argument for that, but I have had an expensive lens dropped when, during transit through airport security, in a bag (with the hood reversed for storage), the filter was shattered but the front element was OK. I also go outdoors for most of my shooting, so my lens may have to cope with rain, dust and potential impact. I also like the idea that a filter may, to some degree, slow down the passage of dust through a lens that extends and retracts.
So, I think protection is important, especially if one has invested a significant sum on the lens(es). I use both hoods and decent protective filters and I am fastidious about keeping them clean and do so properly. So far I am happy that my images have not suffered by doing so, and certainly I consider the cost of the filters a good insurance against paying out for a damaged lens.
@Tronhard wrote:
@TCampbell wrote:
In terms of being knocked or dropped it is often suggested that a lens hood will provide protection and there is certainly an argument for that, but I have had an expensive lens dropped when, during transit through airport security, in a bag (with the hood reversed for storage), the filter was shattered but the front element was OK.
I also go outdoors for most of my shooting, so my lens may have to cope with rain, dust and potential impact. I also like the idea that a filter may, to some degree, slow down the passage of dust through a lens that extends and retracts.
So, I think protection is important, especially if one has invested a significant sum on the lens(es). I use both hoods and decent protective filters and I am fastidious about keeping them clean and do so properly. So far I am happy that my images have not suffered by doing so, and certainly I consider the cost of the filters a good insurance against paying out for a damaged lens.
Exactly. Hoods offer no protection when reversed in your camera bag. I go outdoors a lot, too. My lens filter collects dust, smoke and pollen. I use clear filters on all of my lenses now. I have not found reason to take one off, except for cleaning.
If the clear filter degrades my images, then I say it is a good trade off. Shot with 6D and EF 16-35mm f/2.8L USM.
