When a rifle barrel heats up due to the high temperatures resulting from firing a cartridge, the metal naturally expands as it heats. Pressure on various points along its length from high spots in the barrel channel cut into the stock can cause the barrel to bend ever so slightly as it heats up, which naturally may cause bullets to fly someplace other than where the previous shot(s) went.

Since a floated barrel doesn't touch the stock along its length, that variable is removed from the equation. Sometimes it works to improve repeatable accuracy, and sometimes it doesn't. Floating is at its best when used with rifles that have relatively heavy (large diameter) "bull" barrels, because they are less flexible than slimmer barrels. Lighter "sporter" barrels are less stable, and may flex enough during the shot that accuracy will suffer.