There aren't a lot of people who use them anymore. If you get one for free, like the OP, then it's worth it to have, as on the Interstates the traffic reports can be handy. In the event of a breakdown you could probably get help as well. If you go out and spend a lot of money on one, well, you probably will be disappointed.
Like the OP, I got a free radio. It is a Uniden Bearcat 980 SSB CB, still new in the box, along with an Astatic hand mic, just for helping to clean out a storage unit for someone. It was a case of, "Help me, and take whatever you want as payment." I figured a new CB radio, mic and a new DeWalt 3/8th-inch socket set was well worth a days' labor. I put it in my cargo van, and am now in the process of building out a cargo trailer, and I will put it in there when I finish it. Admittedly, the socket set gets a LOT more use than the CB!
Much like others have said, there is a TON of nonsense on CB radio, especially when the skip is rolling in. When you just have groundwave going, you may not hear anyone, on any channel. Or, if you have a small antenna, expect poor performance. A 102-inch whip is your best bet, if you can do it. Ignore idiots and use the radio as intended, as again, if you got a good enough deal, it can be handy to have. I believe channel 13 is where many RV types hang out, 4 & 16 for 4x4 types, and 19 for truckers. However, there are 40 channels for a reason, and you can find people on all of them, although you're supposed to stay off channel 9, unless you have an emergency. If I had an emergency, and my cell phone wasn't working, I would probably use channel 19 however, as more people listen to that one than probably any other.