Sorry, I should of clarified that I side sliped it to about 300 from about 600ft. No one has told me its a no no in the 172, though I try not to make a habbit of needing to!
I have only had to bring the flap back up once other than the time I was shown, and then it was only back from 30 to 20deg, so the attitude change was pretty small, and I felt more comfortable with my slope than before. I can full see how it would cause large sink going from full flap to none, I dont think I could ever see anyone doing that unless at great height.
I dont know if it makes any difference, but in the focred landing check list, we list flaps "as required" rather then "flaps full" which I heard once. I guess this lends itself more to being able to use them as need be before switching the master off?