Back in 2014 (and possibly still, I no longer live in London) not only was it cheaper per ticket but it was capped per day, so you couldn't accidentally pay for more than the price of a one day ticket. Obviously this is much superior to buying paper tickets for each journey. But I remember having quite a hard time convincing visitors to use their contactless cards on the machines.
Though only on a fixed Monday to Sunday period. So if you arrive and depart mid-week, you might pay up to an additional capping period and buying a weekly travelcard could work out cheaper (provided you know in advance which zones you need).
A travelcard also lets you buy slightly cheaper rail tickets for travel outside of the TfL zones (tickets to/from "Boundary Zone n", with n being the last zone in which your travelcard is valid), whereas with contactless the same trick requires physically getting off the train.
This is awesome. In Canada, GO transit is also capped per day. Unfortunately for me, that cap was something like $20/day when I was really using it frequently.
