[dekhn]

Extra licenses are simply an opportunity cost. Because it's so much work to license software it's usually done in a big negotiation that estimates how many licenses are going ot be used. Further, the licenses are often spread out over the whole org, with various users coming and going, and you want to have enough license slots to accomodate peak users.

(that said, if you can negotiate to only pay for active licenses, that's good)