If it was me I'd be pulling and pushing on that cable end while listening for someting to make some kind of clink clank clunk noise then try to find where they are coming from. If I got no noises and everything, including my heat/AC worked I'd just tuck it back where I found it.
I should’ve concluded this post when I found out what this cable was for, but I totally forgot. So for anyone who stumbles across this post trying to figure it out too, it turned out to be for the blend door like others had mentioned. I wasn’t able to figure this out until I fixed my heater and it started blowing hot air.