John B wrote:

Yes: Kentish Town - Bank - Gants Hill

Is this "touch in at
interchanges" policy just a hoop TfL makes people jump through in
hopes of making money off those who forget to do so?

No, it's a way of allowing people to choose between an expensive
journey via an expensive route, or a cheaper journey via a cheaper
route.

I was surprised to see that for the journey to Gants Hill both Kentish Town
and Kentish Town West (is that where the OP's example actually starts?) are
both defined as via zone 1 . I was half expecting the latter to default to
the cheaper fare, but it doesn't seem to.

Interesting that Tristan seems to believe the new idea is a con, whereas
AFAIAA it was set up precisely because many people believed the previous
system was sometimes ripping them off. Can't please everyone I suppose...

Paul S