In the case of an instructional video, it can really be frustrating to watch 10-20 minutes of something before realizing that the maker did it wrong, didn't document it adequately etc. Those videos tend to have a high ratio of dislikes to likes and that can easily prevent one from wasting their time.
I've been doing a lot of home renovations this past summer and watching instructional videos to help guide me. There's a lot of trash out there and it's not always immediately obvious as so without watching for a decent chunk of time. Conversely, there are a lot of videos with low-production values that are highly useful, so judging alone based on ten seconds can be misleading.