Missile Launcher is a "AOE" unit, his main role is to damage the croud and keep them under fire.
Passive: Stay Away
Blast units back
Active: Back Off
Shockwave that knocks all attack units back
Tactics: passive - knocking back units to line of fire, this effect make the "travel" distance the attacking unit need a bit longer in addition to the fact those units are kept under fire from turrets that could have been out of range.
active - "Back Off" can be really usefull in scenarios where you wish to make sure the enemy doesn't collect your "gold" and you wish to get the enemy back into your fire range.