Matthew P Jones wrote:
I think the fast to and from Amersham trains now stop at Wembley Park
for possible crew changes.

They do.

They never used to and as a long distance commuter, I wish they would not!

I believe that a secondary reason why the fast Amershams started to stop
at Wembley Park in the off-peak was because they were mostly empty,
leading people to complain about half-empty trains zooming through the
station and full trains stopping. Crew changes are of course the primary
reason, but stopping a half-empty train to allow people to get to Harrow
or Baker Street for onward connections probably doesn't hurt in the
off-peak.

This would make it easier for people at Wembley to always know the platform
and the loss of 2 trains an hour can't be that much of a hardship.

This is true, but a decent provision of DMIs would lessen this
particular drawback.