I keep my bike covered as much as I can. Even though I park out of the sun in a carport, there's still a lot of dust and pollutants that gets on the bike in just one day. Plus, especially at work at the store, it keeps kids from thinking it's a toy to play on.
But then I have the Kwikover, which sits in its own bag on top of the back of my passenger seat. Easy to put on or roll up and stuff into the bag. It covers most of the bike: seats, instruments, grips, mirrors and half of the windscreen.
I bought mine from Laminar Lip and I just bought another one right now when I checked their site, as it's almost half off! Check it out:
kwiKover by Laminar