Loose genuine gold leaf sits loosely between thin rouged paper sheets in the booklet. It has to be handled using a gilders tip (brush) and is used to gild onto moulded,carved and embellished areas. Also used for watergilding and glass gilding.
Transfer gold leaf is the same genuine leaf but pressed onto a backing sheet of acid free tissue paper. It is generally used for gilding onto flatter surfaces, for signwork, walls & ceilings and exterior gilding.
Generally easier to use
Here is a video to show the difference between loose and transfer leaf