Bits are a staple of Twitch streaming. They're a way to back a streamer if you can't afford a full subscription, or want to offer some additional support. Until now, though, you couldn't easily buy them on your phone -- you had to either go through the web or wait until you got to a PC, by which point it might be too late. That won't be a problem for much longer, as Twitch is rolling out Bit purchases in its mobile apps. If you want to celebrate a streamer's victory, it's now just a few taps away... for an extra fee.
Since Apple and Google both take cuts of in-app digital purchases, Twitch is charging extra to make sure you're sending a similar amount of money its way. It'll normally take about $10 to buy 500 bits where it would normally cost $7, for example. This is more about convenience, especially for younger viewers who don't have credit cards. If you'd rather save money, the web option will still be around.
The feature will take a "couple of weeks" to roll out to 40 countries, including the US, UK, Australia and much of Europe (there are differences: bits are available only through iOS in China, for example). Also, Twitch is keen to remind viewers that there's more in the pipeline. You can soon buy bits with PayPal, and subscription gifting will be available if you want to treat a friend.