Paul Corfield wrote:
There is nothing I have read that says that travelcard holders
travelling within their zonal validity must touch in and out. The
obvious reason for this is that there is no requirement on such journeys
to activate a claim against the pre-pay purse on the card.

Hello fellow LUL man!

The two reasons I usually give my punters for making sure they always
touch in and out with a season ticket (apart from its easier than
vaulting over the gate...) is that if they don't, 1) they cannot claim
for any disruptions as there will be no record of their journey and 2)
over time if no-one touches in and out, there's no record of their
journeys and services may be trimmed as there are apparently less
people using the trains. Especially in Suburban areas.

I've read through all 40 posts (I've never seen such activity on an
internet thread I started!) and don't think this has been mentioned.
Additional to the £4.00 charge for incomplete journeys, Oyster cards
will now require either a valid season ticket, OR a minimum of £5
credit or they will not function. I believe this is a reaction to the
fact people would stick £1.00 on the card as minimum fare that would
open the gates, then worry about their negative balance later
(something that contradicts the Conditions of Carriage).