Unless using the RV, you retract the slide room.
1. Most manuals will state in high winds/rain, the slide out may leak
2. It will not if retracted
3. Slideouts fail to operate at times. If left extended, then when it fails, HOW do you get it in to the service center? I get these calls all the time from customers that left their slide outs extended when they were not using the RV.
4. You should always extend and retract the slide outs once or twice a month to exercise the seals and keep the seals from sticking. Think of how a Automobile door seals stick if the doors have not been opened and closed for weeks, especially in hot weather.
5. If the slide out has a slide cover, you needlessly expose the fabric to sun and UV and those deteriorate the fabric over time. Doug