The "W" key in the targeting sequence is useful as noted in an earlier post; however, it limits unit fires to only the selected weapon, while firing all the weapons other than the main gun may result in equivalent suppression and even a kill. Given, this situation, say an M1A1 firing upon an infantry unit at 100m and wanting to preserve main gun ammo, right click on the unit, then inactive the main gun. In the case of the M1A1, it will not lay down fires from it's three CMG and AAMGs whereby putting more lead on the enemy than the "W" key sequence.
Note: The main gun should be activated before going to the next turn.
Main Gun Inactivated