I use my rear slider all the time. It is a great way to air out the cab. The window needs to kept clean and any debris kept out of the seals. I also spay some silicone into the seals to keep them lubed up. It helps the window slide easier and the silicone does not attract dirt and grime.
Having the extended cab without a motorized rear window in my last truck I would never open it. It was too far to reach and a pain in the rear.