^^ Depends on how picky you are. The more pump gas you leave in the tank, the lower your overall octane will be when you fill up. As long as you have the same mix every time for your "race gas tune", you'll be fine
As to pros and cons, the pro's are the ability to run more agressive timing, more boost, and just have the overall ability to make more power as long as the tuning is there
Some of the cons though, are that you run into o2 sensor and cat issues if you still have them, cost, and eventually you get addicted
