The only drawback is that researchers need a microfilm reader to be able to consult the microfilm. In either case, the original can be discarded, preserved, or just stored in a vault awaiting future preservation. Preservation photocopying provides hardcopies for researchers to consult. Each copy is bound into a volume for use. This is an excellent option if the material does not receive much use, and there will not be a need to reproduce it in the future.
Many researchers prefer working from hardcopy, in fact.
The major problem with this reformatting option is that only a pre-determined number of copies can be produced at one time. Unless a master copy is retained, an option most institutions will not choose, future copies will be difficult to produce. Whenever it is necessary to preserve materials for the future, preservation microfilming and preservation photocopying should be considered in addition to actual, hands-on conservation treatment. If it is only the information that is worth preserving, then these two options should be considered viable ones. Even if the original must be retained, these options can provide a use copy, thus minimizing the handling of the fragile original.