flap retraction
 

I have noticed on a few videos I have seen in the 777 767 and 757 after landing the pilots will retract the flaps in increments say likeon the 767 theyll go from 25 or 30 to 15 stay there for a few seconds then retract them to 5 keep em at 5 for a few seconds then clean al lthe way up. What is the prpose of this? Why dont they just clean them al lthe way stright to 0 liek o nthe 737s they just go 30 ro 40 stright to 0. thanks,

Tyler