I see players shift-click move their units back and forth all the time in replays online. Why do they do that? Wouldn't a hold position command achieve the same thing?
A unit moving back-and-forth is can be harder for enemy units to kill (especially with melee units).
A common example of this is in PvZ when Protoss sends a Probe to try and block Zerg's Hatchery. If the Probe was stationary, it would be a lot easy/quick to kill it; for this reason, Protoss players shift-click and move their Probe all around the Hatchery location to stay alive as long as possible, thereby delaying Zerg's Hatchery.
The shift-move, or the "queue" command, can have different meanings.
- To scout different locations around the map, so the scouting unit checks out more places and dont go somewhere in a straight line.
- To scout around your own or the enemy base.
- To block off the enemy trying to expand or similar buildings.
- To focus fire a group of units, by killing them one by one. Example: TvZ Shift-attacking Collosi with Vikings has a better outcome than just attack moving into them. It saves you time, and enables you to focus on the other units with your other troops.
- To scout attack, and clean up Pylon, Overlords and such.