Stop Command

The Stop command has very limited uses.

Stop unloading
One important use is to stop the unloading process of a transport unit (medivac, overlord, warp prism) when the unload command has been issued targeting the transport unit itself. There is no other way to cancel the unloading otherwise.

Stop roaming queen
This command is used as a partial solution to the roaming queen problem.

Rewrite chain
It makes sense to issue the stop command right before the beginning of a chain of commands. This way the unit will interrupt whatever it was doing and immediately start to execute the chain. This helps to prevent the risky situation where a unit is issued a chain of commands that are meant to be executed immediately but the commands are just appended to whatever the unit was ordered to do earlier.

For example:

At first, the player wants his zerglings to scout the opponent's base. The player issues this order:

move to the location of the opponents base

On a second thought, the player wants to scout a few resource locations INSTEAD.

there are three ways to carry out this: The first will result in the unit scouting the resource locations AFTER scouting the opponent's base. This could be fine, or it could be a mistake.
 * 1) hold shift, move to the first resource location, move to the second resource location, ..., release shift
 * 2) move to the first resource location, hold shift, move to the second resource location, ..., release shift
 * 3) stop, hold shift, move to the first resource location, move to the second resource location, ..., release shift

The second and the third will result in the unit scouting the resource locations only.

Some may find it more reliable to issue the stop command at the beginning of the chain.

Other technical info
This command can be shift-queued, but it does not make sense to do it unless the unit is patrolling.

Once shift-queued a stop to a patrolling unit, the unit will continue its way to the next patrol waypoint, discarding all other waypoints. Afterwards, it will stop.