SMGs provide great mobility and must be exploited by playing aggressively - they are not meant to be used as a long range weapon or to guard an area. SMGs are the perfect weapon to flank the enemy or reaching a target quickly in objective-based game modes.
These weapons can be used reliably to score kills even when you are not Aiming Down Sights (ADS) due to them having good accuracy when fired from the hip. SMGs ADS quickly and you also stay reasonably mobile while doing so - there's usually no need to use the Stalker perk with Submachine Guns.
