no its not necessary but it reprograms ur ecu to work with the new mod, so its a good idea. All u have to do is unhook the negative battery terminal and let it sit for a couple of minutes and ur good to go. I have done it after i put in my CAI and my exhaust.
even if u dont unplug it ur ECU will eventually calibrate itself for ur mod. Unplugging the negative lead reset ur data at 0 where not reset ur ECU has stored data will eventually will alter to ur mods.