[howardrd]

With each admission to the mrs an actual seat number is allocated. With cash there would be conflict unless the unsold seats were assigned at the turnstile as only season ticket seats are marked as reserved. Other fans who buy in advance, and have their choice of where to sit but their seats are not marked. It is therefore not possible to allow cash paying fans entry to this stand unless they are assigned one of the remaining, unsold, and random seats.
The mrs is primarilly for season ticket holders and those fans who like to choose where to sit in advance. That said there must be an easier way of making any unsold mrs tickets available in the period leading up to kick off.