“The Slip is a maneuverer that can get you in trouble fast, if you don’t know what you’re doing, and I DON”T recommend it.”
No kidding! It can lead to as cross-control stall and a spin “out the bottom” as I recall from my flight training. It’s one thing to do a forward slip in a Cessna 150 with it’s low wing loading and stall speed, but it’s another matter with a swept-wing air transport. With the availability of spoilers on transports, there really is very little if any need to perform a slip. The neat thing about spoilers is that you don’t have to change any of your other control inputs or make changes in power settings. I flew gliders for a while. The spoiler is a very useful control feature on a glider to help you “make the runway” when you don’t have an engine!