I only use torpedoes...so there is PLENTY of time for me to select a different fore and aft target - particularly when the BOPs are circling me. Two torps front, two back...I can keep firing until they're gone. This doesn't work with Romulans, however.
Maybe you can multi target easier that way, but I wouldn't go around equipped with nothing but torpedoes. You're losing a very large arc of fire and better dps against shields. There is usually plenty of time between rounds of phaser fire to multi target with them almost as easily.