Studs are supplied in standard lengths, and tall walls need splices. The usual site method is to butt one stud on top of another and fix a plate over the joint. It works in compression and badly in everything else: the joint has no lateral restraint, the two sections can rotate relative to each other, and the wall shows a kink exactly where the splice is.
The CHC120 connector is a 118 × 43 × 200 mm, 1 mm pressed part with a slot on both faces and a limit plate in the middle. Each stud end enters its own slot until it meets the limit plate, so the splice is set at a fixed depth on both sides and the two sections are held in line. The slots bear on the stud flanges on several faces rather than on one.
The difference shows up as straightness. A spliced stud with a connector is straight in both planes, so the board line stays flat over the full height and the plaster skim does not need to compensate. On a 6 m wall that is the difference between a wall that reads as one plane and a wall with a visible band at 3 m.
There is a smaller version, CHC80 (77 × 38 × 200 × 1 mm) for the 84 mm system, and a QU38 splice for the cross rail. The logic is the same everywhere: a joint in a frame member should be located and limited by a part, not by the fitter's eye and a handful of screws.