I use lanyards all the time
There a retention lanyards that attach the knife or flashlight to my belt.
I carries a folder for years in the army, never lost it.
They are also good for pocket carry of a small fixed blade, so when you pull on the knife the sheath comes out of you pocket only so far, then the knife pulls out the sheath.
There is a loop lanyard, which is a loop to wrap round my hand, or hang on my wrist.
Very good for working and letting go of the knife.
Then there are fobs on the end of a knife to extend the lenght of the knife or to pull it out of the sheath.
In the army we had two lanyards, one round the shoulder iinto the top pocket for whistles, and a neck lanyard for a pistol.