[Imp]

limiting Z fire would need some sort of trust & think could exempt troops as only time I tend to do that is moving adjacent on occasion say in woods. The game makes it that inacurate with no LOS can easily pin your own troops which is correct they are blind firing.
Otherwise Z Fire main uses.
1) Firing through smoke normaly towards targets you had a LOS to, what Z fire was mainly introduced to allow I think.
2) MG is in transit misjudged LOS but important so fire anyway hoping splash hits
3) Soft targets in a group in LOS will Z fire if an empty hex may cause more splash especialy if they are running to keep them at it.
4) Firing at a hidden firer as in someone recieved fire from that hex but not visible.
5) If I know an enemy squad made it near my MG will attempt to pin it as the MG will probably not win the close quarters firefight.
6) On odd ocasion if my troops have blundered into others near by may try & pin them to save my troops from counter attack.

What I think you are objecting to is blind firing all or nearly all every turn just to fire them, I have not come across this very often seems a rare tactic.
Intrestingly as never really thought about all the above with the possible exception of 2 seem reasonable.