I love my Oyster card - so much so that I gave up my Forest Hill rail discount to get one at one point.

It's so much easier to have in the bottom of a bag and just touch it rather than having to juggle a piece of card with the rest of your shopping etc. And it makes going out of zone for whatever reason quicker since you don't have to queue up for a ticket since the ticket machines rarely had extensions on them.

I'm guessing that as well as fines, it also saves costs in terms of the number of gates, ticket machines and men in ticket offices.