+1 on all above reasons. Open in any conditions and while traveling to keep the air flowing.
SIL had not installed one yet as I kept telling them to do so and one night while we were out a few weeks back it poured. Husband looked at me and said OH Crap! I just smiled and said I told you it would happen. Sure enough they spent an hour with some towels soaking up the rain water that was all over the inside of their unit when we got back. Hard lessons are sometimes the ones people need to listen. Needless to say there was one installed upon arrival home.
There are a few options out there varrying in price and all will do the same job so buy what suits your budget. I have had the Maxx airII's on all my units and they perform well. Easy to install and clean.
2014 375 BHFS Eagle Premier
2014 Ram 3500 Longhorn DRW CC
6.7 CTD, Aisin, 4.10's