Slide out awnings yay or nay?

I think it depends on how you use your RV. We park under trees a lot and the covers keep junk from geting jambed into seals (guy is wrong about the wiper blade). They also keep direct sun off the thin roof of your slide and cut heat intrusion tremendously.
If you don't care about either one of these issues then there's not much need for them.

I would avoid them if you camp in the wind regularly.

I added one to my last TT and I ordered them with the latest trailer (which BTW, are JUNK).
I would not go without a cover again but I would elect to install them myself so I know what I'm getting. Even the cheapest model you can buy is far superior to the ones manufacurers might install. If you do order them with the new trailer, getting the alumaguard option should ensure you get quality awnings.

Doesn’t cost a dime to try out your new RV without awnings. After a while, reevaluate.

If you have a bedroom slide where your bed slides out, you will want an awning (Slide Topper) for that slide. On our first camping trip with our 5th wheel we were under trees and it rained hard. It sounded like a freight train. Then when the rain stopped, I listened to drip drip drip drip the rest of the night. Since I put the slide topper on, I sleep like a baby. As for the other slides, I agree with 2oldman. Stay away from camping under pine trees or late fall when the leaves drop and you will have little issue.

The best way to clean your slideouts is to not park under trees. OK, a bit obtuse, but pine trees especially.

I've never had slideout awnings, but I sure don't wish I had them.