Registering is free. It keeps everything you have bought in one place, so a cut you purchased months ago is still a click away.
Every order, its licence and its download in one history rather than an email you have to find again.
Your details are already there, so buying the second cut takes a fraction of the first.
An account works either way. If you are buying for a company, its details and your colleagues can be added later.
Takes about thirty seconds. If you are buying for a business, those details come later.