You can travel around (scanning your contactless debit / credit card) without thinking about how much you’re paying, safe in the knowledge that the system caps your daily / weekly spend to predefined limits, essentially making it never more expensive than a daily / weekly travel card would be. The caps are automatically calculated for the zones you travel in.

It’s a very nice experience as a rider. Especially beneficial to visitors who can just scan through the gates as any Londoner would, no ticket purchase required.

As for the rationale to implement such a system — well, it’s ultimately a public service. All revenue generated is reinvested into the network, in London at least. The economic value of a fast, efficient, painless transit system that everyone uses, regardless of class or wealth, most surely outweighs any lost breakage revenue.