A small part of the puzzle:
Every plane has an IAS where it maintains its best rate of turn, corner velocity. WWII prop airplanes have a problem though. They do not have the power to MAINTAIN high-G turns at corner velocity, the induced drag causes them to dump speed in high-G turns, they can only sustain a much lower rate of turn.
Therefore, considerable thought and trickery goes into how and when to use energy, when to conserve and when to pull hard turns in these airplanes. For instance, at the beginning of an engagement, you will generally be well above corner speed. You could just cut throttle and reef around in a hard turn to get down to corner speed, but then all that energy would be gone and you can't get it back easily. So you can reverse with an Immelman, which kills two birds with one stone by getting the speed down quickly AND putting some of that speed in the bank as altitude.
Air speed is your money in your wallet. Altitude is your money in the bank. Act accordingly.