experimental rules in MBT

[retired from gaming]

I dont care about that rule to much, as I play purchase games only on rare occassions. But I dont understand one very important thing - why FO has to be there until all rounds land ? I never was in the army and dont claim to be an expert, but if I just use common sense and bit of imagination it goes like that :
I am a battle commander and have one FO (or to be more precise - artylery observer, cause he is with me not at the front line, and thats what I reckon was/is in RL based on everything I read/watch). I have an area I want to be covered with arty barrage for long time. So I say to my arty guy : Hey, dude. Call your boys and tell them to fire at x,y until they go winchester. So in game terms, lets assume it will be 15 turns. In the game, because of technical reasons you got to push the button every turn, but we can say it is a battery commander who repeats the order. Why then I cant use my FO to call another strike in another place for 15 turns ?

BTW I play lots of premade scenarios, which are as close to RL as the game can get. And usually (for some nations - NEVER) you wont get any FOs. So why purchase games should be different.

What I am really asking here is - how this rule improved the game ? And I am not buying the answer that it gets rid of people buying to much arty. There are easier ways to deal with it.
And yes, I know it is my game and I can play however I want etc etc etc...