The visual effect might be akin to the tracer effect on phasers, or perhaps there glow on both particle weapons and projectiles is an effect of the fictional subatomic particles and physics effects described. For example a by product of the rapid nadion effect in phasers might be the orange glow or blue glow depending on things like energy input or frequency of the phaser.
The point is that no matter how you rationalize it, it's still wasted energy. Any realistic design process would try to minimize that waste. As a rule, you don't want your device to glow any more than it
has to glow. You don't want a propulsion system to radiation energy in all directions, because that's stupid and wasteful. You want it to direct its energy toward the rear, where it's useful.
You're taking the way it looks as gospel and trying to justify it. I'm saying it shouldn't look that way to begin with, that it looks that way because it's a fictitious special effect designed to make the weapon visible to the TV/movie audience, and that in the "real" underlying universe of which the TV shows and movies are dramatizations, it might not actually look that way at all, because the standards of film creators and the standards of real-world engineers often work at cross purposes.