Dave Arquati:
Out of interest, why did they decide to have a slow/fast separation
here and how was it used? Did trains skip either/both of these
stations, and if so, was it really worth it?

Clive Feather:
Yes, many District trains skipped various stations, including both
Gloucester Road and South Kensington.

In 1964 there were 8 non-stop trains in the morning peak.

This is, of course, the Underground's special sense of "non-stop",
meaning "not stopping at all stations" as opposed to "making no stops
between terminals".
--
Mark Brader, Toronto | "[i] have a will of iron."
| "And a head to match." --Robert B. Parker, "Chance"