One big reason I like vent covers is for the additional "storm protection" they offer.
A few years ago when I worked at a local RV dealer, we had a bad hail storm pass through our area. We had about a dozen "stick & tin" style RV's that came in for repair estimates that ended up being totaled.
But the big demand was for replacement vent lids. We sold out every one of the more recently made styles and even sold some new vents to replace older ones I couldn't get parts for. It was a couple or three weeks before we were able to get enough vent lids in stock to meet all the demand for people who needed them. Many people had to put plastic bins over the top of their broken vents to keep the rain out until they could obtain replacement lids.
I also sold several vent covers since they add a 2nd layer of protection from hail stones, falling tree branches and such. If a hail stone punches a hole in the vent lid, then there is nothing to keep the rain out. But a vent cover usually is much heavier duty than the flimsy vent lid. It will deflect blows that would penetrate a vent lid.
I like the opaque colored vent covers since me and Mrs Tail_gunner like to sleep in while we're camping. The dark vent covers help keep that annoying light out in the "too early" hours of the morning.
FAA A&P mechanic, ex-RV dealer parts dept
Retired B-52 Gunner/Flight Examiner, B-52 Crew Chief
2016 Jayco Eagle HT 29.5 FBDS w/ 15,000 BTU AC, 50 amp service, upgraded counter top, thermal pane windows, elec. stab jacks, outside grill, backup camera and MORryde pin box.
2011 GMC 2500HD DURAMAX/ ALLISON