The launch also includes a Stream Summary feature that shows your viewership stats from previous streams, including data that contributes to your Affiliate and Partner goals. If you want to know how many new followers you got when playing a new game, you'll have a simple way to check. This also includes insightful stats that can help you grow your audience, such as the sources of your views (say, a fellow streamer or Twitch's game directory) or the most popular clips.
It's no shock as to why Twitch is offering these tools: it needs to encourage as much broadcasting as possible, and that means offering help to streamers who want to turn their gaming (or creative work) into a job. If you know just where you need improvement, you may be more likely to push toward pro status instead of treating Twitch as a hobby. This doesn't make the road to paid streaming any easier (you still need to be a good host and promote yourself to the hilt), but you'll at least know when you've reached your destination.