In the original game, you had to have LOS to a hex to do direct area fire (Z fire). It included actual visibility in that computation, which of course is nonsensical. If you can brass up a particular corner of the field in front of you with your machine gun in daylight, then in night time it is simply a case of dialling in the appropriate elevation and azimuth off your range card and pulling the trigger.
We changed that so that the LOS is the absolute one, as if any smoke, night or other obstructions to vision weren't present. As it should be. Thus its the weapons arc that is used, with a little bit of scatter added allowing penetration of cover.
Direct area fires are a standard military tactic, with the Americans in WW2 having been noted for the vast amount of ammo they used up in blazing away at anything that might give cover (Reconnaissance firing I think they called it?)
https://en.wikipedia.org/wiki/Reconnaissance_by_fire. But the British soon were using as liberal an amount of such fires when advancing down bocaged hedgerow roads. The Russians would do this with unlimbered field guns firing over open sights, or SP guns. Firing direct HE like that removed the delays of indirect fire calculations. I too like to use my SU-152 firing direct area HE at points my main force is advancing against, on the attack, as speculative fire.
And it also serves for the usual laying of machine guns on fixed lines in the defence - another standard tactic. When you thought you were under attack (usually at night) then you would hose down known avenues of advance. So in the defence in low visibility, I often fire tripod MG in out front of my defence line just beyond the vision level to break up potential attacks once I suspect he is close.
It uses up ammo somewhat, and has less than half the effect of an aimed shot at a detected unit, but is valuable in certain circumstances. Also if you do not have sight to the target hex, there is more chance of scatter for firing blind.
Against a human opponent though another reason not to do it is that the firers ID and location will be given away, so tagging those for retaliatory arty barrages. Or simply telling me that a whole company is at that point that I had not known about - thank you very much for the free intel, mate!.
The AI also treats Z-fire as an "item of interest", just as with manual smoke popping or regular aimed fire events and thus it will tag the launching hexes for arty stonks on occasion.
However some players take it too far - hence the house rules found in some PBEM games limiting its use.