Why would he fire on an empty hex when he could fire on that same hex when an actual unit moves in?
JR
Meant to respond to you earlier, but technical difficulties intervened.
So to answer your question...sure, absolutely,
most of the time it makes sense to wait for an actual unit to shoot at.
But there are cases when you would definitely prefer to fire ATT at the empty hex. Ideally you would need three conditions... 1. a single hex choke point like a bridge or minefield clearance etc. 2. A number of units which must get thru that choke point.... 3. who are individually difficult to hit... hitting the hex is easier.
In that situation I think you'd rather have a decent chance of putting meaningful residual in the bottleneck hex than take a terrible chance of hitting the first unit moving thru the bottle neck -- but that's not an option... the issue here, as you pointed out and which I had failed to appreciate, is that ATT HE doesn't leave residual unless it scores a hit against a moving unit (*edit, nor attack PRC collaterally).
Imagine you've got an exit VC game. You are the delaying Germans, The Brits' only hope in this, their last turn, is to exit 5 infantry laden carriers down a woods road going full speed ahead and they can't lose one infantry VP! But they are almost certain to succeed. Due to the rather bad position of your 81mm mortar you'll have just one glimpse of LOS (1/2 mp) to take your one shot at the carriers. You will go for a shot against the lead carrier... but you'll have to pay Case J+2 and Case P +2 to get an initial hit and leave residual so at say 5 hex range you'd need a "unlikely" DR 2 to hit (the +1 woods don't help until you get a hit!). At present this would be the only option. I think an interesting and possibly tactically sound second option would be to be able to hit the hex (either as prefire during the Mph or when the first unit moves thru the choke point) scoring a hex hit by hitting without Case J or P ... so in my example a DR 7 hits, leaves residual and will attack all those juicy vulnerable crew, passengers, and exposed riders as they pass thru the hex with ATT residual 4fp +2 PC + 0 Rs. (Hope I resolved my example correctly, LOL).