I cant see how a lanyard on a knife would be useful. I must be wrong or the manufacturers would not make knives with a lanyard holes. What is the experience of the INGO members with lanyards and how do you use them if at all?
My ESEE 6 I use the lanyard hole for a small length of paracord to wrap around my wrist so I can hold it lower on the handle and maintain leverage and grip when I am chopping with it. I'm pretty sure there are some YouTube videos out there that people have put out showing exactly what your asking about.
For folding knives, other than the aesthetics (coolness factor) of having a lanyard, it can be used to help pull the knife out of the pocket. It does help especially with a knife that is designed for deep pocket carry. For fixed blade knives, it is more of a safety and control feature. With a lanyard around your wrist you are less likely to lose control of your blade when using it hard.
Slip your thumb through the lanyard, wrap the lanyard around the back of your hand, and grip the handle. If the lanyard is the right length the knife will not come out of your hand. (The right length for me before tying is around 27".)
All of the guys that have responded are right about the uses. There are a lot of other reasons though. Youtube or a knife forum are probably your best source for the info.
Several of my knives have lanyards and many do not. It really depends on what I use a specific knife for. My hunting and skinning knives do not, but most of my bushcraft type do have. PM me if you want a more detailed explaination.
I only have one on my Lionsteel SR-1. The pocket clip carries so deep, it's hard to get it out of my pocket. I don't like them at all to be honest, but sometimes they're very functional.
Slip your thumb through the lanyard, wrap the lanyard around the back of your hand, and grip the handle. If the lanyard is the right length the knife will not come out of your hand. (The right length for me before tying is around 27".)
This is how I do it as well. It has the advantage of helping lock the grip in your hand when you are using it, plus you can easily let go in a hurry if you need to release the knife quickly. That's not possible if you put the lanyard around your wrist.
It was also the basis for the way I tie and use lanyards for flashlight use, aka "the rhino wrhap."
I have also used them for other useful things. Once to replace a broken shoestring in my boots when hiking in El Paso. Once to tie off an emergency candle to a stick to make a torch, when my batteries died while camping. I'm sure I could have done a lot more if I had thought about it.