[k00pa]

Fuel usage is 0 when you slow down without brakes... When you use brakes your engine needs fuel to idle. (Assuming you are using manual transmission, and on automatic you can force down the gear to do the same.)

[RobotCaleb]

Some cars even stop fuel flow if you're in gear but not applying gas.

I think it's called Deceleration Fuel Cut-Off (DFCO).

[Toucan]

When I use my brakes I don't put the car in neutral until I'm almost stopped. The fuel consumption is the same.