Another is to pin the maps down onto some corkboard. The worst thing to do is to tape the maps down. The tape will stick to the map and tear it when you try to pull the tape off. Maps with small pinholes can be listed as mint or excellent, those with stuck tape can not. Most better gamers use Xacto knives to get counters out of a countersheet.
Some people also go an extra step and use a nail-clipper to clip the edges off the counters.
Both methods are fine. However, if the counters were pulled out of the countersheet and a number of them are ripped or damaged, the game can no longer be listed as mint or excellent. Because most gamers do careful punch or cut out counters, most counters will be in excellent condition. Charts are altered, rules are highlighted, and coffee and beer mug stains are evident. In these cases, the game can no longer be listed as mint or excellent.