What problem does this address?

In Trac, @mindctrl notes:

It would be nice to include some throttling detection for when browsers lose focus and/or don't have typing/activity in some period of time. I left a couple clients open for ~7 hours for testing and this caused over 230k post meta writes.

What is your proposed solution?

Add inactivity detection based on the number of updates send by the current client and reduce the polling frequency accordingly. Some suggested parameters: No activity in the last 30 seconds, reduce polling to once every 5 seconds.