[Nick 95 6sp]

In addition to the reasons already mentioned above, the stock ECU on the TT Supra (at least the post '93 version I'm most familiar with) does learn some things. For example, if it detects knock it is very aggressive at retarding timing as an initial protective reaction. So for people who consistently exceed "safe" limits of boost for the octane they run, with the ECU pulling timing it results in sort of a "wet blanket" feeling and the engine isn't as responsive or powerful as it could be. So if that happens and you reset the ECU, that resets the timing to the factory default (pretty aggressive) settings and that has noticeable beneficial effects in this situation. People who operate in a manner that causes this pulled timing consistently report quite a few mph improvement in 1/4 mile trap speeds by reseting the ECU.