The new feature to automatically scan for new question activity using web sockets is a potentially handy feature, as it reduces the need for refreshes, and makes information available faster. There are some cases where it would be beneficial for users to be able to turn it off though:
Keeping an SO tab open at work: at some workplaces where the internet may be monitored or filtered, having a constant connection open to an SE site might raise flags.
Mobile devices: for people using a mobile data connection (tablets, smartphones, etc.) with a metered connection, having a constant data connection running may use up data without users intending to do so.
It's really annoying: some people just don't like having a tab yelling at them
(15) new questions!!when they aren't asking for it. It's distracting, and I'm sure there are others who would like to be able to turn it off.
For most users it's a nice addition, but there are definitely situations where it would be nice to turn off the auto-updating.