I don't have any commercially available rails on my machine so this may not apply but anyway; I would do all that is practically possible to keep the crud away from the rails. When I am using my machine I am constantly wiping down the rails or using compressed air to blow away any debris. It needs surprisingly little to jam things up, especially when it is aluminium that is being machined I also try to keep the junk off the screws and out of the nuts as it is my opinion that this may act as an abrasive and wear things out sooner. I may be wrong but this is my opinion.
I think that many commercial rail systems have a wiper that clears away debris from the rails but it would be better if you stopped it from getting there in the first place.
I hope this helps and also hope it is correct!