Clive D. W. Feather wrote:
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?

But how would going one extra stop and then detraining avoid any hold
up? It would just mean the hold up would be delayed by a couple of
minutes.