As for watching streamers play a game, I'm not really into that. I have watched some gameplay videos on UT if I'm having a problem with a boss battle(
@Brian Boru there's those bosses again), or a particular difficult section of a game, but it's kind of rare, as my first step is to consult a Wiki or similar source. For both sources, it's really a last resort, as I'd rather figure things out myself if at all possible.
With the gameplay videos the quality can vary greatly just by the narrator's voice, and how well they enunciate their words. Some are great, others, not so much. I remember watching a video years ago, where the narrator sounded like he was eating from a large bag of chips and spraying crumbs everywhere, I could barely make out his words. I had to turn that one off.
Game announcement videos, as well as gameplay videos from the game developer; I love watching those if it's a game I'm interested in, or if I'm undecided about buying it.
help guides - there are a lot of good videos for learning.
This very much so. Back when I was first learning to mod games, I watched a lot of UT videos on certain aspects of modding, and they were extremely helpful. There's several videos by a modder named Gopher that are very helpful, detailed, and presented in a logical way. I still watch some of those vids from time to time If I'm doing a fairly large mod order.
Just last year when I was modding FO4, I was having a certain problem with a mod called We Are the Minutemen. Found a short UT video by TheAldipose that showed step by step instructions how to solve that issue by using FO4Edit. For things like this UT can be a great source.