By separating the legal process from the ceremony, restrictions over content, venue and costs are removed.
Treating legal marriage registration as separate from ceremonies and celebrations, in the same way as we do for births and deaths, means that you do not have to have a Registrar or a Religious Officiant present at your wedding ceremony. This, in turn, means that you can have your ceremony in an unlicensed venue, which reduces cost, quite dramatically.
Your ceremony can take place a couple of hours, days, weeks or months after the legal registration at the Register Office. You are then not restricted to a set legal format, which also allows you to incorporate spiritual language, music and literature, these are not permitted in Registry offices, or Licensed venues with a Registrar present.