Rachel Andrew with a clear (get it?!) explanation of
display: flow-root;, including demos comparing old and new techniques. Apparently the name is still a little bit still up in the air.
The whole point of it is getting rid of clearfix, or using a different/unintended property for float clearning. Every time this is brought up, there is always a well actually about how
overflow: hidden; does the same. Like we mentioned before, overflow has consquences totally unrelated to float clearning, like hiding shadows.
Source: The End of the Clearfix hack?