The benefit is that you don't need to wait for verification from the user that they got the packet before you can send the next group of packets. If you're, say, watching a stream, it's not important that you received the packets because that's just a few skipped frames or a second of lag, whereas the tradeoff on overhead is pretty big.

TCP is more important with like file downloads where it's okay if it takes a couple hours to get a really big file as long as that file isn't corrupted or missing any data.