PSA: To the "everyone needs to group" crowd.
No, no we don't. When I solo push down top inhib and then put so much pressure on bot lane that they have to send their fed Zed and high impact team fighting Rumble just to deal with me while their Vayne deals with the super minions we don't need to group. The rest of the 4 of you need to learn to utilize the map pressure I have created and get your backsides mid lane where all you will deal with is the support and the jungler in a 4v2 instead of wasting time picking your nose and killing raptors.
There is more than one way to play the game than the "lets group up and smash our face into the enemy face" strategy. Learn to use map pressure and take objectives instead of running around looking for kills and wasting time.
EDIT--Because rereading it I noticed I didn't really state my position very well. I'm not saying to never group, or that grouping alone is bad. This came out of my last game in which the only lane that didn't lose was me, but my laning opponent was a rumble so it did't matter he lost. That left our team of Yi/Vlad/Ziggs/Lucien/Sona to try and deal with teaming fighting a fed Vayne/fed Zed/Jax/Rumble/Nami. We lose that easily and the only chance we had was to split and exploit the map pressure I could create.
Is it always the way to win? No. But in this case it was our best option but people wanted to get caught up in the "we have to group and team fight" BS to focus on actually winning the game.