I add enough weight to get it balanced then a 1/4oz here and there to aid in the driving performance. If the club doesn't enforce a weight rule then I will run my car as light as possible. A lighter car has less tire wear, is less prone to breakage hitting stuff at speed, accelerates & stops faster, the list goes on an on. If you do run light then you need to know how to adapt your setups for the lesser weight.
If you plan on running regional and national events then you should practice at the weekly club races with your car setup to be legal for those events so you are use to how it performs at that weight.