The last two posts in this thread indicate most pool cleaners have more longevity by leaving them submersed. I cannot scientifically challenge that but it seems to me not as logical as removing it.
A suction cleaner or a booster pump cleaner has no onboard motor so waterproof seals are non-existent. A robot, however, has onboard electrical and must remain waterproof in critical areas. My assumption is that chlorinated water will take a toll on those seals and eventually cause them to fail.
Maybe not, but seems to make sense. Over a long enough period of time, chlorine can begin to eat away at many, many things.