10 degree flaps increase our lift, reduce stall speed, reduce ground roll. Seems like all advantages with no disadvantages. So why does the Cessna 172 POH say normal take off is 0-10 degree flaps? Why not always use 10 degree?
Flaps out will reduce the ground run, but you're forgetting that they also increase drag. This is why you don't climb all the way to cruise altitude with flap extended. A 172 will climb better without flaps.
With a take-off, you have to consider both the ground run and initial climb. After all, the take-off distance required is defined as the distance required to climb to screen height (50ft in Australia, sorry if the US is different). The aircraft also has to meet a legal minimum climb gradient to that height.
Without looking at the data, it is possible that in certain conditions, taking off with flaps 10 will get you off the ground quicker, but will actually take longer to reach 50ft compared to a takeoff with no flaps. In any case, retracting flaps in a busy time after takeoff is a potential hazard, and in a training aircraft like the 172 simple procedures are best.
With 10 degrees of flaps and the trim wheel in the "take-off position" my C-172 will rotate without any back pressure on the yoke. You have to apply forward pressure to keep the speed above 62 knots. A flight instructor a few years ago during a flight review suggested I always use 10 degrees of flaps during take-off. After using this method for a few months, I concluded that using 10 degrees introduced a new hazard. A stall during take-off was more likely. I went back to 0 degrees flaps.