I would want a retention lanyard if I was working up in the air or over water where dropping a knife would mean it was gone forever or someone could be injured. Some people like short decorative lanyards, often woven from para cord. Some even claim that these are useful in various ways. I remain skeptical, but figure I should try them and get first hand data.
I will point out a risk with a simple short loop of paracord. It is the perfect thing to get caught on a branch and yank the knife out of your pocket without realizing it. Anyone who doubts this does not spend much time hiking off-trail. I am almost certain this is how I lost my original Benchmade griptillian.
Tom's Knife Info / firstname.lastname@example.org