What are the advantages of grouping/teamfighting in League of Legends?

I'm coming from Dota 2 background, and all I can see is that teamfighting seems to be ridiculously risky. If you win the fight it's great but if you lose it's pretty much over because there's no-one left to defend and because the buildings in League die so much quicker than in Dota when your team is all dead you'll lose so quickly.
I'd say a lost teamfight isn't that bad pre 25 second death timers in League but as soon as it gets longer than that you may as well just spread out over the map because even if the enemy gets a pick off on one or two of you it's better than the entire team and meanwhile the rest of your allies will be getting farm.
Best Answer
If the opposing team groups to push one of your lanes, then you have to group to defend it. One or two people are not going to feasibly be able to defend against four or five.
By the same token, if you have an advantage in map position and the opposing team is still spread out, grouping will allow you to quickly push down the last few towers.
Team fights also happen around objectives like Dragon and Baron, where the team who brings more people to the fight is often the victor.
There are inherent disadvantages to grouping, such as a lack of presence on different parts of the map, and that if you lose a team fight it can be catastrophic to your chances of winning the match, but a lot of times the alternative is simply losing the match without putting up a fight first, which is even worse.
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What is comp in lol?
Introduction. Team Compositions (or team comps) can literally refer to the five champions that a team chooses to play in a game, but they can also refer to overarching classes of team comps. Depending on the champions chosen, a team will have different strategies that they employ in order to win the game.How do I get better at team fighting?
A front-to-back teamfighting composition is a long time classic of League of Legends. This composition consists of a group of low damage front-liners that are there to engage and peel for their back-line of damage carries.How to Teamfight in League of Legends: ULTIMATE Team Fighting Guide!
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Answer 2
The answer is in your question - just like you said 'the buildings get destroyed faster' so if they have 5 pushing a lane there is no way 2-3 people can hold it and because the loses to your towers/inhibs/positions will be SO detrimental and so quick you have to plug the hole with most if not all of your teammates else you risk losing a lot of things without being able to take anything yourself.
A little bit of farm for 2 other people isn't greater then the enemy team getting towers and possibly an inhibitor - they get EXP and gold for those as well and if they are pushing as 5 against 2-3 they will take 1-2 towers and maybe an inhib giving them a HUGE increase to farm compared to your team being split and getting a far less increase which puts them in a position to just steamroll objectives, bosses, and the rest of the game. Not to mention your risking some 'easy dives' in lane by having it so poorly defended which will only increase their farm/gold/xp more.
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