I guess I can pose the same question for top lane because it's pretty much the same idea anyway. Your lane roams elsewhere to get kills, but should you punish the XP and try to damage the turret while he's gone or go after him? How is your decision impacted by how ahead or behind you are in lane?
Mid lane decision making 101. Tbh when i'm mid and i see someone leave to roam i usually spam ping MIA all over the map and hope my team survives while I take down the free turret. I figure if he wastes his time and fails to get kills, or overstays i'm punishin' the XP and at least threatening an objective. WBU?