Ideally you want a large pot with few players. Yes you must always be favourite pre-flop with AA, but that edge decreases with the number of opponents - particularly if they will all go to showdown.

Another point to consider, which is possibly less relevant at 0.02/0.04, but important as players get stronger, is what hands would call/reraise a raise (e.g. KK-TT, AK-AQs/o), i.e. the hands against which you are strong favourite. Allowing limpers in (and BB for free) increases the range of hands you may be up against. This means that you won't know where you are with many flops. So don't be surprised to lose on occasion to raggedy 2-pair or runner-runner straights and flushes.