In message , Clive D. W. Feather
writes
If you're planning to detrain a southbound service at Finchley Central
and run it empty to Highgate depot, why not let it continue in service
to East Finchley and detrain it there? That way you won't hold up all
the following trains while the driver walks all the way down to the
back and then to the front again.

Or is there a logical explanation for this instruction?

Yes, they've done away with the guards who only walked from the back to
the front.
--
Clive.