There are a lot of functional factory sheath knives available. But one thing that renders many of them less than ideal, is simply the sheath.
Here is one example of a factory knife (the Ontario Spec Plus Next Generation SP42) that, for some users, can be much improved by a custom sheath.
Note how the leather sheath rides high on the belt, and how the factory, military-style sheath hangs fully 4 inches lower! If you want the factory sheath to stay with your leg instead of swinging like a pendulum, you’ll want to use the leg tie. (One more thing to do when taking it on and off.)
Also, the factory sheath has a retainer that is fastened with a snap. The leather sheath uses a cam-lock in the welt to secure the knife, which is a hands-free system that works very conveniently and dependably.
This is not to say that the factory sheath is bad. In fact, this is an excellent factory sheath, getting an “A” for safety, and a similar grade for compatibility with military carrying systems.
However, as an individual who likes to carry a knife this size every day (and has, for the majority of 15 years), I can tell you that around the house and on the farm, the leather sheath would be my preference.
Another reason for custom sheaths, is for situations where a knife simply does not have one, such as this vintage WWII-era PAL RH51 Remington Hunter Boy Scout knife.