As others have said, you could one day find yourself in an emergency where this remains the last available option to extend the glide.
I'd say the technique of using flaps for energy management in a power-off approach is both safest & most useful in types with manual flaps where there is no significant pitch change with flap retraction; the tomahawk & hershey-bar cherokees are obvious examples. If your flaps are electrically-driven, in a real emergency, you'd likely want the master switch off before you reached the point where manipulating the flaps in this way would be helpful.
If you have the right type of aircraft, I think it's a technique worth practicing; the last thing you want to be doing in any emergency is trying something out for the first time
-though, again as others have said, not with passengers
.
It's also one way of achieving a precision spot landing from a glide approach. It's a long, long time ago now, but I remember using the technique (in a PA38) during this part of my initial PPL skills test - and since I passed, it must have been acceptable to my examiner.
But I'm struggling to think of a valid reason to retract the flaps during a normal powered approach - the throttle is your primary energy management
control.