You don't have to use it the life of the engine, it just means that if you change the percent then you have to retune.
Well I didnt know that. I had a bad experience going to 30% nitro to 20% on my picco .28 p3 on my REVO The engine started running really sluggishly and didnt wanna go more then 25mph. The throttle would open full but would only get 1/2 power.