Very few people buy portable buildings. The idea is that since they are transitory, need-based constructions, you don't want to own them and deal with the maintenance. Typically, people rent these, and those who purchase them are persons who work as contractors.
During construction, contractors utilize them as temporary site offices. When the capacity to build new permanent schools is exhausted, schools use them as temporary classrooms. Some individuals use them to create an additional office in the center of their factory or warehouse.