I do it whenever I get stuck, but since my definition of stuck also includes "irritated", "impatient", and "bored of this puzzle after poking at it for 45 seconds," I tend to use walkthroughs a lot.
Sometimes, I will walkthrough the first level or two of a game, just because I feel like I'm not really getting the internal logic of the game. Then, once the lightbulb goes on in my dim little head, I go all the way back to the beginning and start over, playing without reference to the walkthrough unless I get stuck, and by stuck, I mean really can't figure something out. Most often this is because I'm just flat missing some visual cue. My vision is probably no better or worse than most people with glasses, but I'm not very good at looking.
Sometimes, I will walkthrough the first level or two of a game, just because I feel like I'm not really getting the internal logic of the game. Then, once the lightbulb goes on in my dim little head, I go all the way back to the beginning and start over, playing without reference to the walkthrough unless I get stuck, and by stuck, I mean really can't figure something out. Most often this is because I'm just flat missing some visual cue. My vision is probably no better or worse than most people with glasses, but I'm not very good at looking.