Op fire filter question.

[matxer]

I'm still puzzling how to use this new feature (outside ambushes, which Grumbler described well).

The most obvious use I see is for ATGM. ATGM ammos are low (generally 4 to 8) and each time you fire, you run the risk of being detected.
So you want the juicy targets only. It makes sense to filter out the soft targets (trucks), the scouts and armored troop carriers (low armor) to save the shots for the MBTs, doesn't it ?