It's probably more about figuring out who's shooting you than whom you're shooting at. And they may be more helpful than you think. Some game elements may not seem important consciously, but even a minor bullet effects could make the difference subconsciously. Regardless, there's got to be some reason that the devs implemented tracable rounds, as the alternative (hit scan) is much more simple to implement and easier computationally.
If nothing else, the pulses make the game more visually interesting.
I'd say the reason is because they thought it'd be more visually appealing (which if most weapons are hitscan as Malanek says seems to be the main reason), and still, it bugs me.
In ME (1) there is a bluish "smoke" you can use to trace who's shooting you, and you can see if you've hit your target since there also a bullet-impact effect ,all while bullets are barely, if not noticeable at all.
In the end, I realize I can live with visible bullets as long as they travel as fast as in the first ME
With all the hit scan weapons (which is most of them) you are only seeing a trace. The computer does the hit resolution as soon as you click the mouse.
mmm really? I could swear I saw targets dodging bullets in both ME2 and ME3
I suppose I'll have to replay them
In any case, I'd prefer faster traces anyway