Different units have different tactical roles in a battle. If you're aware of how this sort of thing works, you can use it to enhance the realism of mass combat scenes in games. If you care.

And if you don't care, no doubt one or more of your players will be all too happy to point out the tactical flaws in your NPC troop deployments.

(In future, you should recruit that player to help you plan the NPC side of the battle.)

Transcript

R2-D2: The Gungaboo River Valley has the lowest fixed gun placement density, so we fly along that to the target.
Luke: The what?
R2-D2: That squarish trench. The Peace Moon was never fully landscaped, remember?
Leia: R2, I hope you've taken those PIE fighters into account in your calculations.
R2-D2: What? Ha! No. Just dodge them.
Leia: X-wings: take care of those fighters. Y-wings: into the valley.
Luke: Shouldn't I fly in to torpedo the vent?
Leia: You should... if you were flying a Y-wing bomber. Note the word "bomber", as displayed prominently in the profile data. Now take out those PIEs!
R2-D2: Hey, who do you think is in charge of this operat—
{beat, showing Leia in command of the mission control room on Yavin}
R2-D2: Okay, never mind.