I ocassionally use a lanyard of a fixed blade knife if I am using it in a situation where I may loose it, but usually I find they get in the way.
I do have another use for a lanyard though, to get my folding knife out of my coat pocket in the winter. I find that in the winter when I am bundled-up in heavy clothes it is hard to draw your knife from a belt sheath, so I keep a folding knife in my coat pocket. Then the trouble is that my big pockets are full of other stuff and it is hard to find the knife, expecially with gloves on. So what I do is attach a 2 foot (arms length) piece of paracord to my knife (lately a German Military SAK) and to the button-hole of my right chest parka pocket. It makes it easy to withdraw the knife with one hand (even without opening the pocket), and I don't loose it. The added benefit is that people rarely ask to borrow your knife because it is attached to you. A fixed-blade knife carried in a sheath suspended by a neck lanyard (like Mors Kochanski) would serve the same purpose, but would draw a lot more attention (unwanted in my case).
I have another very small knife that I keep in a new EDC mini-kit I am working on, the knife fits in a slim pocket and was hard to draw, so I attached a small figure-8 knot of paracord to it and now it is much easier to get it out of the pouch. I have been working on this new kit for a couple months but started carrying it before I completed it, thats why I have not posted it on the forum, maybe I will finish it soon.
Mike