My Jayco 5er came with them. They go on top of the slideout when retracted and lock it in position. Its basically insurance in possible case of the slideout accidently deploying whilst taking a turn or curve on the freeway.
In he 30 years I've been RVing...I've never seen or heard of such an incident happening.
I put a yellow velcro "Caution" sign on the slideout switch to remind me when the braces are locked in place on top of the retracted slide.
The other reason for using the braces is that it snuggs up the slide out to the RV...keepig rain and dust out of the RV while moving...and that does make more sense!
