I'd rather their be no auto fire at all and only barrage, placing a mortar/leig/pit etc 'safely' in a contested area and having it fire whilst you micro elsewhere is too cheesy for me.
If you want to use your indirect, use it.
There is already the safety vs accuracy dynamic. A mortar firing safely from max range isn't worth it as the accuracy of indirect units is rather bad at long ranges. If you want to get value out of a mortar, you already have to micro it to stick closely behind your units and manually target / barrage the units you need to hit.