I grasp and understand the concept, but I am admittedly guilty of this. I usually kill strongs first because I can wipe then out in about 3 seconds flat. Elites and above though, I ignore until the weaker enemies are taken care of.
Well damn. If you can down the usual lvl 50 strong that fast, you should be able to one shot ANY normal/weak. Which begs the questions why aren't you?
Frankly, any DPS worth a hoot should be able to take out norma/weak mobs in 5 secs or less. On my sniper, I can easily 1-2 shot them (a crit from Ambush will kill just about any normal in the game, and if it doesn't Follow Through will finish it off; in FP's this means one less mob inside of 3 secs, timed right=simultaneous with tank's pull), strongs usually in about 3-4 shots. The advantage being near immediate reduction in group damage. On their own, the normal mobs hit like a limp noodle, so damage from them on DPS is (or should) be minimal. (Think death from a thousand needles) I have also found that when I am tanking a strong or elite and the DPS is also attacking the same mob, if I have to go off the strong/elite to taunt a normal attacking my healer, I quickly loose aggro on the strong elite because aggro generation in SWTOR is not like other MMO's where tanks can hit a mob once and never loose aggro.
I remember my Tankadin in WoW could run a gauntlet of mobs, tag everything once and have it follow me thru half the dungeon. Can't do that in SWTOR.
Another thing to consider is, in the 3-6 sec's the DPS is working on the normals while the tank is on the elite, that is 3-6 seconds of aggro lead the tank is able to build on the DPS when they finally get to the tank's target. Which means, DPS is less likely to pull aggro and tank's Guard can be where it belongs, on the healer.
While leveling, the same strategy should also be used, kill the weak stuff first, quickly reducing the overall amount of damage taken. It is why I like leveling with HK-51 and his Assassinate skill (one less mob to do damage on me before the fight even starts).