I go both ways. If it's a good playthrough, or a good game that I won't play, then sure. Especially if I enjoy the commentator, or their skill. I watch Game Grumps play through games pretty religiously. Game Society Pimps are really good, heavy edits, but they generally make their own stories out of games, which makes a boring Skyrim long play into something random and hilarious

Then there's the games that I've super enjoyed and I like to see what others think or it, or how they deal with things differently in the game than what I'd done. I have really so far enjoyed Super Best Friends play Bloodborne, and Freedom Planet. And watching Markiplier play through Alien Isolation, and both him and I loved the game. In these situations I've usually beaten the game, or played way farther ahead than their videos so I don't get anything spoiled. And sometimes I'll avoid videos entirely if I know it's something I intend to play soon