For the main quest, I have used them occasionally, but only as a last resort. Everyone probably has a different idea of what qualifies as being "stuck". For me, if I've spent 3-4 hours trying to figure out where to go or who I need to talk to in order to advance, then I'll probably end up consulting a walkthrough. I really don't like to use a walkthrough on the main quest, so I'll wait until it really feels like a lost cause before consulting the walkthrough. If I'm stuck because I'm sucking at the game (bad strategy or bad timing/pattern recognition) then I'll usually just keep fighting through it.

After beating the game is a whole other story. I usually like to get all the collectibles, and I'll make an effort to collect as much as I can on my own, but there comes a time when I don't have the patience to continue scouring the world for things, especially if I'm not even sure how to acquire said items. So I generally consult a walkthrough for optional content at some point after beating a game. I still like to do things on my own, but I don't press it as hard after beating the game.

Depends on what it is, usually I don't but it's something extremely obscure like in Mega Man 7 when you need to use Rush Search to find some hidden items. I'm not going to spend all day looking through every nook and cranny to find one item.

Depends on whether I get frustrated or not.

Yes, if it's anything like SMG2's green stars

I only resort to using walkthroughs to find collectibles I missed and only after I have beaten a game. I enjoy the challenge and beating the game feels more rewarding if I figure it out on my own.

Almost every walkthrough I have seen is useless. I can always figure out better techniques and ways to accomplish the goal or beat a level on my own.

I don't necessarily consider using a walkthrough cheating though.

Majora's Mask is near impossible to 100% without a walkthrough
So yes

Yes i do always but only after i tried everything and waste like 1 hour. Only view games i could beat without looking on youtube, these were metal gear solid 1, 3 and 4 from what i can remember. Thats why the metal gear series is high quality games despite being so complex youre always able to beat them on normal defficulty. Its dueto the codex.

There are other older games i have beaten without any help but that was during the times without having internet.