An improvement to supporter perks, you can now choose your broadcast resolution. Currently, the options are from 240p, 480p and 720p but more could be added at a later date. Choose your quality setting either in the source selection pop-up or in your user settings.
Additionally, you can also set the stream quality to receive, reducing all cams to a lower definition. These options should allow for better network performance on mobile data services, or if you just want to conserve bandwidth.