As a kid I lost pocket knives that fell out of my pocket, so I started using lanyards attached to a belt loop. Clips help keep your knife with you. Sheaths will do the same thing, but I don't like sheaths on belts for pocket knives.
I have pocket knives with clips, w/o clips and with sheaths. The WH pocket sheaths are a good compromise and I am always surprised that so few custom makers take that route. It gives you a clipped to the pocket knife, easy one-hand opening, but no clip on the blade.
I often just carry a knife in my pocket, but with nothing else. That works until I forget
For pretty knives, I will use an in-pocket sheath or a WH clip sheath.
The worst clip is one that was not designed for the knife, just bought and screwed on. A lot of lower end or new custom makers do that. I like makers that inset the clip attachment point into the scale, like Terzuola and he even carries over to many of his factory-made designs. For many clip designs, insetting the attachment point makes them easier on the hand. That being said, Michael Zieba has some interesting clips and they are quite ergonomic but not all are inset.
A knife designer needs to think ahead and plan the clip just like they plan the rest of the design and build.
I have pocket knives with clips, w/o clips and with sheaths. The WH pocket sheaths are a good compromise and I am always surprised that so few custom makers take that route. It gives you a clipped to the pocket knife, easy one-hand opening, but no clip on the blade.
I often just carry a knife in my pocket, but with nothing else. That works until I forget

The worst clip is one that was not designed for the knife, just bought and screwed on. A lot of lower end or new custom makers do that. I like makers that inset the clip attachment point into the scale, like Terzuola and he even carries over to many of his factory-made designs. For many clip designs, insetting the attachment point makes them easier on the hand. That being said, Michael Zieba has some interesting clips and they are quite ergonomic but not all are inset.
A knife designer needs to think ahead and plan the clip just like they plan the rest of the design and build.