For reasons that have (at best) a limited relationship with rationality, I always have a filter in front of my SLR lenses and only sometimes have one in front of my rangefinder lenses. If I'm not using a circular polariser on my SLR lenses (and usually I'm not) I'll put a clear filter (usually a UV filter) in front.
The only filters I use on my RF lenses are there for effect: generally an ND filter (sometimes I like shallow DOF on lenses I use with my M3, and a 1/1000thSec shutter speed sometimes doesn't cut it) but other times it might be a yellow or orange filter, or even a red one (I assume those are faster, like red sports cars).
I'll plead a limited sort of rationale: in general (but far from always) my RF lenses are "better" than my SLR lenses in terms of optical quality. (So why put a filter with a less-well-attested piece of glass in front of 'em?) And yet, quite often (for high-end modern autofocus ones) my SLR lenses are more expensive. Less need to worry about optical quality, coupled with higher replacement cost. Also, I tend to worry about filters more when conditions are bad (dust, sand etcetera). Perhaps that's why I use filters on my SLR lenses, as many are zoom lenses so I don't have to change 'em so often when environmental conditions are difficult.
On the other hand, I use clear filters on my SLR prime lenses, even when I seldom if ever take them into harsher environments.
You can probably see some sense in the above, but also some reflexive irrationality. And if you can't, I certainly can. Suffice it to say, I'm a simple-minded kind of guy, so I tend to a simple rule: SLR lenses get clear filters, whether they need them or not. RF lenses don't. Unless there's an important reason why they might need one.
...Mike