I usually watch playthroughs when I am really interested in a game already.

No, I normally look for reviews rather than pla throughs. That being said, one of my favourite games (Tokaido) is one I discovered from a Wil Weaton playthrough

I'll look for a short sample of what the gameplay looks and feels like. But that doesn't give info about the whole play through (unless you watch the whole thing from start to end). A review should tell you what the progression and experience is like from start to finish in a much more summarised way.

Yes, generally as a last step before buying (often after a review). I mostly watch Heavy Cardboard and Before You Play, for the slower pace and higher quality (some rules people talk to fast for my taste).

I like reviews better, but I have watched a few playthrough videos when I really want to see it go through its paces, or if there are people playing that I enjoy. Favorite review youtubers - https://www.youtube.com/@BoardGameBollocks

I don't have the patience for playthrough videos. I usually try to find a text review and read the parts where the reviewer talks about the general feel of the game, what they like and what they don't like. If I find the concept interesting, the art good, and the cons not too bothersome, I go for it.

https://youtube.com/@3MBG

Don't have the patience for full playthroughs so I usually watch 3-Minute Board Games. This guy from New Zealand does reviews of games in 3-4 minutes. That's his whole schtick!

He does a good job explaining the basic rules of the game and his thoughts on it in a very succinct manner.

I can usually get a pretty good feel for if I'll like a game or not after watching one of his reviews and I've discovered a lot of lower visibility gems I normally wouldn't have otherwise considered from his channel!