We request the following permissions from Twitch:
bits:read - For historical bits information
clips:edit - For creating clips directly in StreamerKit
user_read - General user info, we need this to be able to identify your channel, from your login.
user:edit:broadcast - That's the "stream key" one, I believe. Not used for anything right now, the hope was to interact with extensions using this.
chat_login - Whispers, eventually!
channel_subscriptions - Guess ;P
channel_read - Getting info from your channel, specifically view count
A lot of what we're asking for is "We will likely need this in the future for possible feature X" - we don't currently collect any data from your channel automatically, and we'll tell everyone if/when we do!