I have had them on most (if not all) of my previous RV's, however they didn't come on what I currently own which I have owned for about 6 years now. I wonder how many of us here who feel they are very important to have actually have had an RV without them and used it for a year or more w/o awnings? I ask because I have never once had water come in, the seals on mine are in great shape still, I am able to clean the top whenever a lot of dust settles on it (try that with an awning in your way). When I had the awnings, I had issues with water puddling on the top, wind causing the awnings to flap, I couldn't get under (between the slider and awning) very easily, had a bird build a nest where the awning and edge of the slideout meet, had to replace the awning material after 4~5 years of age due to tears and small holes. I also discovered on the 5th wheel I owned last, that the slideout seal wasn't very good to start with, the awning cover did help with that... but not completely as I would still get some water intrusion until I fixed the seal (it wasn't installed correctly).
With all that said, they do what they do, so I am not against having a slide-out awning, point being is that because mine didn't come with one, and I decided to wait and see if it was really needed, I determined that I haven't encountered any issues with not having one. I suppose if I was camped under trees where small to large limbs could fall that the awning would keep the limbs off of the slideout, but on the other hand, tree limbs falling on the awning likely would be an issue as well, especially after a few years and when the awning material gets weaker. Perhaps pine cones wouldn't cause much harm.
Don't get me wrong, I am not opposed to slideout awnings, my opinion is simply that they are not as valuable (for me anyway) as many people believe they are. In other words I wouldn't remove them if mine already had them, but now that I have gone without them, I wouldn't install them either. I still suggest to the OP and others, if yours doesn't have them, give it a try and make up your mind after a season or two. It is very affordable to go without them to see how things work out before purchasing.