You shouldn't ever have to resort to raising flap to reduce float. This is an artificial reduction in lift, rather than just flying the a/c correctly.
Why shouldn't we play with flap in the flare?
1) Assymetric flap retraction.
2) Pitching movement caused by movement of the centre of pressure.
3) Time. How long does flap retraction normally take?
4) If you are floating, you normally have too much speed, so if you retract drag flap, you will slow down less quickly. On Cessnas, the 40 flap setting is not there to primarily increase lift, but to increase drag. So why would you get rid of it?
Fly the machine correctly and you won't have to resort to daft things like retracting flap in the flare.