Starcraft – Why do players float buildings around with troops

The benefit of this fancy micro is to 'run and gun'. Marines have a set attack speed, meaning if they are standing still they will shoot, stand still, then shoot again.

So by moving between shots you can constantly be moving away from melee attackers you can kite them (prevent them from hitting you therefore taking far less damage) while still doing the maximum amount of damage (because you shoot every time its off cool down). This becomes even more effective when you mix in mauraders with their concussive (slowing) shells.

To answer your question, this can be extended to ANY ranged unit in the game. It is very common with hellions, thors, marines, and mauraders with Terran

To do this micro, right click away from the enemy unit (ordering a moving command), press the A (attack move command) and left click (this will cause your marines to shoot anything within range) then order another move command; repeat.

Hope this helps!

What you are referring to is the SCV Halt command (hot key T). By issuing this command you can regain control of your scv and issue a movement command (moving it to safety) without canceling the building. Another SCV can then be right clicked onto the building to finish it.