We leave ours on all the time. And have been for the last 7 years. However I did just have to change out my little transfer switch last week. Not sure if leaving it on had anything to do with it or not. My reasons for leaving it on is we have the fridge and freezer full and running 365 days a year, ready to go when we are.
If the transfer switch is working it switches over to shore power when your plugged in. We have not had any issues with the 1000watt invertor at all. Knock on wood !!!