Not sure why you are having trouble seeing that difference…
If you do not need the bomb to trade territories anymore, why not SBR? You’re not gaining anything special by using a bomber if you also have enough fighters available to trade. I’m certain the Germans require their bomb for intensive trading for the first few rounds, but after that it doesn’t seem necessary. So you rack up the first few rounds of risk-less work, then you go off and deal your $17.5 damage. That can be super helpful because after a point all you’re doing is trading 2 territories with Russia which only requires figs, and the bomber isn’t helping very much, so you might as well help Japan by doing more damage through SBR.
And you STILL have the BOM alive to add punch to those major attacks, like sacking Moscow, where it adds 2 kills per 3 rounds of combat.
What I have trouble seeing is how battles last that long. It was difficult for me to see this at first, but very few battles last 3 rounds or more.
So long as the BOM lives, your opponent cannot leave unguarded TRN’s within range
This is about irrelevant past a certain point. If you can tell that having a single bomb no longer threatens the Allies transport chain, then it’s time to send it to SBR. I see no reason to conserve a bomber if it no longer significantly threatens the transport chain and also its services are no longer required except for some minimal change in % for trading.
I’m having trouble seeing why you want to save your bomber past the point when it’s just not helping much anymore, when your figs are capable of handling the trading and there is no more reasonable possibility of threatening navy. You might as well help Japan out by bombing 17.5 IPCs out of Russia, because you sure aren’t going to get that many IPCs out of your bomb when it comes to the final attack, and remember this is after the bomber has served its useful life in trading territories, when you have lots of figs available to do that.