I voted no, because there wasn't a "depends" but there was an "if it..".
Taking advantage of a bug/mistake in a public multiplayer game is not something I agree with. If you use it to beat your opponent then you've proven nothing at all. If you exploited an MMO, for example, to get thousands of gold in seconds then you risk harming your server's economy and it's generally a direct breach of any form of play policy. It's not big, it's not clever and it doesn't gain you anything. Example would be Ensidia/Exodus, two of the top guilds in the world at WoW. Both guilds have negative reputation for possibly/admitting to using bug exploits to get their world firsts.
If it's multiplayer but on a private server with friends, then I don't think it's as harmful (e.g. everyone has the best guns) and it's just a bit of fun. You're not affecting anyone or causing any ill harm.
If it's single player and you're using a bug to circumvent another bug then I don't really see much of a problem. You're only cheating yourself at the end of the day. Whilst not a bug itself, I used the console to give myself items in Fallout 3 (Nuka Cola Quantum, Bottlecap Mines as an example) if I knew I either couldn't get them anymore or I just didn't want to spend hours retracking my steps to get the items I need. I've not, however, used it to give myself items that I cannot find (e.g. weapons in the game files that are unattainable) or to make myself more powerful.
Would GTA be as much fun post-completion without the cheats/bugs? No, I don't think it would.