I think you'll find the stock answer to be, "it depends on your CYA level." The pool industry is always going to quote 1-4ppm as the "all the chlorine you'll ever need!", and so all of their answers will be based on that (4ppm MAX).
The long answer is that CYA, even at modest levels, greatly reduces the concentration of active chlorine (hypochlorous acid and hypochlorite anion) in the water. It is the active chlorine that will degrade plastics and cause chemical wear and tear. But, at the levels advocated here on TFP (FC/CYA ratio of ~ 7.5%), the hypochlorous acid levels are so low that it will not appreciably affect the lifetime of parts in your robotic cleaner given that it is only in the water for a few hours each week. That being said, the chlorine present in your water as either active chlorine or reserve chlorine is always available to react with with the materials the cleaner is made of. So, in that sense, you do not want to leave the cleaner in the water all the time. I have left my suction cleaner in the pool 24/7 and i can honestly say its probably degraded faster than it would otherwise if i took it out more frequently.
It's also one reason why having a manual vacuum is a good thing - you can manually vacuum during a SLAM, or other chemically imbalanced events, and not have to worry too much about elevated chlorine killing your super-expensive robot cleaner....
