Other advantages are that bought costumes can be modified if necessary, and they may be kept for future use. The only real disadvantages are cost and the availability of what you want. A pulled costume is one that is taken out of a theatre company's stock from past productions. The primary advantages are that there is no cost and the costume can be modified if required. There really are no disadvantages except that being limited to stock costumes may require some artistic compromises.
Most professional costumers consider borrowing both unprofessional and unnecessary.
The advantage is obviously that there is no cost, but the risk of damage and replacement expense can undo that. Actors will sometimes request that they be allowed to wear their own clothes. Costumers hate it when stars insist on dressing themselves. During the research phase of the design process, costumers undertake the same sort of collecting of visual materials that set designers do. Since clothing is the only subject, their search is more narrow.