Well a quick google search could bring you to some answers, but for me, ICOs are good because:

• No regulated exchange -> low fees, little delays
• You can get large discounts when buying in bulk and/or early.

For the founder of the ICO:

• Almost no restrictions to the kind of venture he is trying to fund. (depends on jurisdiction)
• Can get huge sum of money. (in fiat currency !)

But never forget the risks, since everything is based on trust and reputation. No required asset securities -> you could loose everything.

So for now, everyone is testing the waters, and only time will tell if ICOs will persist into the next decade.