it differentiates in that is serves two purposes.

1. Being a cut off valve as mentioned.
2. Providing a "PRESET" amount of proportioning or delay to the rear brakes.

There are valves that do one or the other A. bypass valve for isolating the leaking side. B. Proportioning valve for delaying application of the rear brakes.

The pictured valve does both, hence the term "Combination valve". These types of valves are typically non- adjustable so one has to be careful when selecting them as they may or may not work as desired in a modified braking system depending on a bunch of other variables.