After a certain point what's it really doing? After a certain point the Allied transport system is too strong to be threatend by 1 bomber, after a certain point solely your fighters will suffice in trading territories.
Yeah, the bomber isn't always there as overkill. I rarely have a situation where the bomber is truly unnecessary for offensive operations.
Then what's the use of doing nothing with your bomber?
In reality, it isn't just doing nothing. It's presence alone is enough for the Allies to adjust their moves because it's threat range is so large. SBR's may be a wash on average value of the bomber vs. damage done, but losing it to AA gives the Allies more freedom of movement everywhere
and that is a value that you can't easily measure in IPC's, but it is significant enough for me to want to preserve the bomber until the very end.
Remember, in my KJF test game against the Commander, I purchased a second bomber with Japan. On paper, it may look like a risky purchase based on it's high cost, but I guarantee that every move she made in Asia and the Pacific took the range of my bombers into account. That's the true measure of a bombers value, and it's worth every penny.