James Farrar wrote:

What it is probably meant to eliminate, in fact, is people finding an
open gate and not touching in, thinking "if there's an open gate at
the other end I'll pay nothing, the worst that will happen is I'll pay
what I'm supposed to".

Depends on where they are going and whether there is a touch-in option
further along the line.

For example, someone with pre-pay using First Capital Connect at any
station north of Finsbury Park might simply free-ride to Finsbury Park
or Highbury & Islington then touch in there and complete their journey,
thus paying only the fare from zone 2.