To me chair rails are a personal preference. We used them in our kitchen remodel. I like it that we could use two colors on the walls to tie them into the backsplash. If you like a chair rail then leave it up. Also, there's nothing that says that you can't leave it up and paint the walls one color.

I have it and I'm tired of it. I don't hate it, but I'd rather have chunky crown and no chair rail. However, it's useful for our vaulted rooms where crown is problematic. At least it provides some interesting detail. It's also nice with beadboard below for a cottage-y look.

Edited to add: we have used just one color above and below the chair rail.

If you have wainscoting or you have a wallpaper you like or the two toned wall is really enhancing your decor then chair rails can be useful. But just to have this horizontal line dividing everything for the heck of it is out, imo. Now if you also do a paneled treatment above the rail, well that's different.

The ones we have seen on Design Dilemmas lately haven't really had any function, they just split the wall in half, so the consensus has been to remove them and paint your walls one color.