See above, some call them limb risers, helps displace things that could knock the exhaust stack off, or similar. They usually have a package installed on the tractor, limb risers, brush cage screens and so on, also engine side curtains, belly pans, all needed if you work in harsh terrain, brush or similar. Even then you can get stuck with protruding sticks or cut off brush, nasty work at times you have to really watch, go slow til things are cleared.
I pulled a vine somehow with my D7 while heading down a steep incline, I had cut and severed everything by hand prior to, chainsaw, loppers etc, and don't you know a cut off dead piece of elm came up and nailed me right in the side of the head, but hard, lucky I have thick skull, man that hurt, like getting whacked by a piece of 4x4, of course this was an old open station, they don't belong in the brush, me of all people would know since I was an operator full time for almost 5 years, worked in all this stuff before, miss one thing and you are not protected, it will get you. Where that piece came from and how it got to me I'll never know, I had to set the blade down and take a breather, was headed down to get a stuck tractor out.