Although, personally, I never see a reason to keep extra metal or crystal around. It's not like you earn interest or anything. So all it can do is let you build faster after having built slower for a while. Assuming you build at a constant speed the entire time, instead, the result is essentially the same unless you are wanting to on-demand crank out a fleet or some turrets in a specific location apl at once. But I tend to spend all my resources on fleet building, then pause all and build turrets for a hit when needed, then resume fleet building. And stuff like that.
I've been meaning to respond to this.... Obviously there is more than one valid strategy to achieve victory in AI War, and I do think that intentionally keeping reserve resources is a valid strategy, and not just a failure to make use of your income. I heavily employ reactive defense, where in contrast to proactive defense, I intentionally keep spare ship cap, turret cap, resources, and sometimes even knowledge hanging around so that I can swiftly and successfully react to virtually any and all threats, expected or unexpected. This strategy has worked exceedingly well for me on 7/7 with territory footprints both large (hubs/realistic) and small (vines/tree).
That's not to say that I don't employ a fair amount of proactive defense as well, but I have yet to lose a 7/7 game (I only ever lost on lower difficulties when I was still learning the game), so I think my strategy works very well. Naturally it can sometimes make my offensive maneuvers require more care and thought, as opposed to being able to just bludgeon my way wherever I please, knowing that I have the economic power to absorb any mistakes or heavy losses, but it is well worth the added hassle to protect my precious reserves, as the AI has yet to prove that I am anything short of untouchable as long as I have them.
