The benefit of this exercise is its stability. Since you have a bench for support, you can keep your shoulder blades locked down. This prevents your shoulders from moving around and allows you to direct tension through the triceps. Using a cable means you can generate fairly constant tension throughout the rep, so it challenges the entire range effectively.
Seated Cable Cuff Triceps Extensions
The unique twist with this exercise is the use of cuffs rather than a hand-held attachment. When the load is taken out of the hands it's easier to focus on contracting the triceps rather than just moving the weight from A to B.
Because you aren't gripping the weight, your focus is able to shift fully to the triceps, rather than gripping hard and focusing on the hands as you do with regular pushdowns.
This isn't an exercise to be chasing PRs. Nobody cares how much weight you use. But it is an exercise that'll help you develop a fantastic mind-muscle connection. This helps generate a great pump and leads to massive triceps.