I want to reiterate what
@SkiBam @volklgirl and
@Skier31 have alluded to and make sure it doesn't get lost in the discussion.
Yes - sideslipping is a great basic "safety" skill to have in your back pocket. Check.
BUT - understanding how to flatten (unedge) or "feather" a ski - the skill you work on when you are sideslipping or doing falling leafs - is something you employ in EVERY parallel turn that isn't a pure carve. The flatter the ski, the smearier the turn, and also, the easier it is to rotate the ski with our legs and get it more quickly across the fall line - both critical speed control mechanisms.
So HOW exactly do we get the skis to slip sideways down a slope? I'm surprised how so many of the videos don't really or don't fully describe how to actually make it happen.
1) You must be standing on parallel skis with your weight fully committed to the downhill ski. Do NOT lean up the hill as the mechanism to start sliding. If your slip becomes a "one-two" sidestep, you are not committed enough to standing on that downhill leg.
2) To start the slide, pick what works for you. Think of either:
- pushing the pinky toe side of your downhill foot down
- relaxing your downhill ankle and letting it collapse against the outside of the boot (I'm an ankle feeler so this is what works for me)
- tipping your downhill knee out to the downhill side.
3) Once you start sliding, be sure to keep the uphill ski slightly tipped to its pinky toe side or it will catch in the snow.
4) IMHO, really good sideslipping is done from a countered position - that is, with our upper bodies facing down the hill. But lots of instructors teach sideslipping with the skier square on the skis - facing their ski tips. Try it both ways. I like the fact that facing our upper body down the hill makes it easier to get and keep our weight over the downhill ski. Facing the ski tips tends to allow more weight onto that uphill ski.
Practice to both sides. Then - the real reward! Bring that ski flattening feeling into your turns!!! So for me - if I want to smear a turn, I relax the ankle of the leg I'm standing on - the outside ski of the turn - so I can flatten and feather the edge. It makes turning and speed control feel effortless.