What is Scan-Move?

From wikia:

Scan-Move is a command available to units without an attack, such as high templar and the medivac dropship. The hotkey used is A, the same as the attack command. Using scan-move "orders selected units to move to the target area or follow the target unit. Scan-Moving units will not engage enemies."

I don't understand this description. What's the difference between scan-move and normal move? If I scan-move a high templar ... what will he do when he runs into enemies?

Also, now that I think of it - assume I have a group of units selected, where some have an attack and some don't (e.g. Zealots and High Templars). What actually happens when I hit A-click, and they run into some enemies?

Solution 1:

The tooltip for Scan Move:

Orders selected units to move to the target area or follow the target unit. Scan-moving units will not engage enemies.

Scan-move allows the use of auto-cast abilities. If using a regular move command, the unit will not use auto-cast abilities.

Also note that the default hotkey for both scan-move and attack is "A". If you have a regular unit with an attack, and a unit with scan-move as orders, and you group them together and use the hotkey "A", the game will try to execute the attack first. If that order is successful given, the scan-move is then executed.

E.g. If you have a marauder and medivac in one group, and you use the "a" hotkey and left click on a zealot the marauderwill attack the zealot, and the medivac will scan-move to the zealot. If the zealot moves away, the medivac will follow it.

E.g. If you have a marauder and medivac in one group, and you use the "a" hotkey and left click on a mutalisk (remember marauders cannot attack air units), the game will display the error "Must target ground units", and the medivac will not scan-move to the mutalisk. Here is a list of units, from melee maps, with Scan Move as an ability:

• Warp Prism
• High Templar
• Infestor
• Overlord
• Raven
• Medivac (only this unit has an auto-cast ability)