A frame (and mount) gives the artwork definition. It separates the artwork from the surroundings and draws the eye to the focal point.
If the framing is doing it’s job properly it should complement the artwork so effectively that it goes almost un-noticed.
Other reasons for getting things framed include protection of the artwork and to allow it to be attractively displayed.
It might be that (for example) a certificate of insurance needs to be displayed for legal reasons in which case a very simple frame would be appropriate.