Except, of course, when it's standing at a bus stop, engine idling, a big capital investment doing nothing while drivers are obliged to collect a fare from everyone who boards.
Which makes the news of Bristol's own tentative venture into smart card fare payment systems more than welcome.
ULink, the UWE-operated services, have led the way in this; the innovative courage of their transport staff, and their ability to see their role in wider terms than short term operational profit, are something that the reactionary First bus companies should have taken on ages ago. After all, First runs on a vast scale, with near-monopoly in many towns and cities. For them, the potential benefits of switching to a more efficient fare collecting scheme are far greater than any development costs.
Not that Bristol's smart card trial is in itself going to speed the buses up much, it will simply show up any flaws in what's a very simple system. So far as I can see there's still a cash option on the buses, and every passenger will need to declare where they're going and be issued with a ticket, so that the right fare can be deducted from the card.
This is a million miles from the complexities, and the beautiful simplicity, of London's Oyster card. With that, you can pay-as-you-go (knowing there's a cap on the cost each day, however many trips you make), get a travelcard covering the zones of your choice for the period of your choice, or even an annual all-London bus pass (bit of a nightmare thought, that). You can buy it pretty much anywhere, including online. You can use it on the tube, the buses, the trams, and, these days, on suburban rail. And you won't hold everyone up while you get a ticket.
Of course London has a massive advantage over Bristol, in that it has TfL (Transport for London) commissioning most of the services, the rest being the 'heavy rail' train operating companies. We just have a sprinkling of small bus operators, two big bus operators (both owned by First) and the trains (almost all First Great Western, though Cross Country's Temple Meads - Parkway service shouldn't be forgotten.) Without a Greater Bristol Transport Authority (a prospect kicked well into the long grass by the dinosaurs of our neighbouring councils) trying to negotiate cross-modal, multi-operator ticketing with daily fare caps and period concessions will be a nightmare. After all, there's little sign of the three First companies talking to each other, let alone co-operating with any of the other players.
NB. Discovered in the course of writing this....
An annual bus and tram pass for the whole of London costs £664.
An annual bus pass for First services within the built up area of Bristol plus Keynsham costs £784.