Not sure what "supposed to" means; all I can say is that it's not uncommon behavior for racers once they graduate to stiffer shells, was originally recommended to me by a coach. I do it every time I get into my RS130's, not known for their flexy shells. So do other people I know who own the lace ups. It's really easy because the material of the liner seems to slip nicely against the shell plastic, and when the lower shell halves push into top of my instep - ouch moment if just wearing socks - my liners are firm enough to just push back, so I slip in, push hard and whoosh. The heel comes down pretty straightforwardly. You have to keep the sides of the shell open with your hands so you slide all the way to the front of the boot smoothly, but there's none of the wrestling with where your toes are because they're already positioned and encased. The other advantage is that your shell and liner dries out nicely each evening without heroics.
It may be that Langes are easier, or that my foot shape (very narrow heel and ankle, wide forefoot) lends itself to seating easily. I have a 12 mm shell fit, so not about having lots of extra room for slipping in.
My liners show no signs of damage or unusual wear from it. Intuition says one can lose the laces or keep them, obviously if you lose 'em you'll have issues about getting into the shell.