Well, that is a novel way of preventing yourself from frogging past the particular row!
However, here is one good reason a REAL lifeline is useful: it prevents all the other stitches from slipping, or popping, down a row below when you're trying to pick them back up.
Sooner or later, you have to unravel (frog) the entire row(s) down to the 'marked row'...and you're gonna have a lot of "live" stitches sittin' there, just waiting to escape.
A real lifeline lets you zip your "picking up" needle right on through...no one escapes...and then you continue on your merry way...leaving the lifeline in place until you're sure you're never gonna need it again as a safety net.
I still vote for the real lifeline.
I use a long piece of DMC Pearl Cotton for lifelines. It's really easy to install, and it's really easy to zip out. Word to the wise: use a really long lifeline. I like mine to hang out at each end about 12". No joke.