Originally Posted by ninbushido
Guardian Angel is useful for some AP champions who have to be in your face, like Katarina, Swain maybe, Galio.
Late game it's used for a mix of resistances.
It can be annoying and snowball a team further, but think about it this way: a properly positioned team will be able to catch someone out and pop their GA, and quickly kill them even after the GA ends. For example, if that Vayne decides she can 1v5 your team (she can, but y'all did the right thing and CCed and bursted her down), she now has to escape...one Caitlyn trap under her corpse and her fate is sealed.
GA is so much of pubstomping and snowballing hard, though in high-elo and competitive play it's also very useful because of teams being able to coordinate well.
The counter to GA is consistent damage output, preferrably in an AoE. An Akali can be hard shut-down by a GA since she now can't burst the carry to 0 and get ult charges, but someone like, say, Anivia or Orianna or Swain won't really care too much (that's why in so many tournaments, Anivia Orianna and Karthus are used so much because they are late-game carries with either very good DPS, hard CC, supportive qualities, or a mixture of them all.
Guardian Angel can help a winning team snowball very hard and end the game early. Guardian Angel can also help turn games around for the losing team too. If you're that Vayne on the team who has farmed well enough for Boots, IE, BT, and PD, but the rest of your team is not doing well, don't give a s.hit about the enemy's armor and grab that GA instead of LW.
You are now more durable and can hopefully carry a bit better and turn the game around with the hypercarry that is known as Vayne (you have true damage anyways). If you're a well-farmed Cait, abuse your range and grab a GA for the safety. Orbwalk like a pro (see Doublelift's skills...) and you can be the sole carry of the team that helps your team out of the bad situation for the win.
Guardian Angel isn't a terrible item...I depend on the item in many cases as it is a source of mixed resistances. It has multiple uses, both for winning and losing, and though it can be annoying, I believe Guardian Angel is a balanced item.
ftfy, and you wasted all that time explaining yourself when it's still an item many people find unfun to play against, with no counter-play, and rewarding sloppy play that could otherwise potentially turn a game around. It makes coming back either too hard, or too easy for teams that turtle. It has no purpose other than protecting the most valuable teammate (adc) from bad positioning and from being shutdown in snowball mode OR make targeting bruisers even less of an incentive to waste your time attacking.