This would allow distributors of video works to reduce their costs. They would have a choice about whether to accept the risk of getting the classification wrong, or whether to pay a premium to avoid that risk. Alternatively, to err on the side of caution (e.g. to apply '18' to a release just to be safe — even though that may restrict the market).
This would be beneficial in particular for distributors of works with a small audience, e.g. foreign-language video works, small-scale drama productions by local amateur or student groups. These distributors would then be able to work legitimately within the UK economy whereas at the moment such works can quite easily and legally be brought into the UK but only by personal import (i.e. individuals ordering them over the internet) or by downloading.