Mining pools exist for the dreamer with an old computer. He might live in his Mom's basement with an old gaming computer with a loud fan. He wants to mine up some Bitcoins but doesn't have enough money to buy a dedicated rig. Mom will pay the electricity bill, that's good. He just needs to get a few dollars together so he can ask Jennifer out to the movies again. Maybe this time he will get lucky. Last time didn't turn out too well. Sure he's only getting MH/s , but maybe, just maybe, this month he will find a superblock. Solo-mining is tough...especially when he just needs some money.
Seriously though, pool mining gives miners an opportunity to get a steady stream of income. Solo mining would require significantly more risk and waiting for a super block to get a quick payout. This might come next week, next month, or not even next year!
I have been "solo - mining" on Steemit for a few days and have earned 0.0000 Steam.
Meanwhile, you have crap like this on Youtube going viral....sigh. Well, my 7-year old son thought it was funny. LOL