The clove hitch is one of the most-used knots in technical climbing. It attaches a rope to a carabiner (or any cylindrical object) with two wraps that lock against each other under load. The major advantages: fast to tie one-handed, easy to adjust without untying, easy to untie even after heavy load, and works in either direction of pull.
In climbing, the clove hitch sees its main use at belay stations. The leader arrives at a multi-pitch belay, builds an anchor, and clips into the anchor with a clove hitch on the rope. The clove hitch lets them adjust their position relative to the anchor without untying β pull rope through and the position changes; lock it off and they're secure. Belaying the second from above with a clove hitch is also common.
The clove hitch has one weakness: it can roll if the load shifts to a different angle. In climbing applications this is rarely a problem because the load direction is usually consistent. For long-term static loading, a bowline or other secure knot may be preferred.