Some couriers, e.g. Royal Mail, only accept parcels up to a certain size (specific dimensions, or volumised). There is currently no way to exclude those couriers from the selection process for shipments where the dimensions are too large to ship with that courier. Only weight is taken into consideration.
This would be very helpful! Especially if charges for couriers could look also factor in the parcels dimensions, as some couriers add surcharges based on the dimensions and not just weight.