The way I understood it was you can top as many times you want, but each time you do you split the hormones that make the top cola the top cola. So you get more tops, but they aren't as good. I personally would just top once.
Each time you top you pluralize the buds out to more and more budsites. Unless you plan to give enough veg time to recover, you can expect tons of little buds and few or no big ones. Not that that matters if the overall yield is unaffected. Size of buds has nothing to do with potency.