'Land after' enables a safe clearance to be issued and prevent an otherwise unnecessary missed approach. Would a clear landing clearance with associated distances as per Doc 4444 be more appropriate, possibly, however the 'Land after' procedure works well and helps the ATCO to provide a safe service. The important aspect being that the 'Land after' clearance be issued in good time and as GT3 says, not be upset by the potential for a missed approach if that is what the crew desire.
2.5nm spacing is a robust tool to enable consistent throughput to the landing runway in stronger winds.