I leave them in, in fact I try to drive on gravel roads as much as I can so I can fill in the tread with rocks and make my tires last longer. They also make good traction on ice and snow when they're "studded" with rocks.....
2004.5 GMC SLT CCLB, Ride Rites, Turbo brake, EFI Live
2012 Arctic Fox 29 5T 5th Airborne, B&W, Prodigy
Papillon navigators Lily, Buddy and Willow