Okay, poor choice of words using 'clearance', sorry.
It does not change the fact that the 'Land after' is a useful procedure to enable a pilot to safely land when otherwise a missed approach would be the only option. The Part 1 is quite clear that:
'the runway is long enough to allow safe separation between the two aircraft and there is no evidence to indicate that braking may be adversely affected'.
The instruction (I appreciate that some won't like the choice of 'instruction' either) would not be issued if the mandated condition's were not present.