A Whitelist is a list of websites that lives on your computer that you want RescueTime to pay attention to. If you visit any web site that is NOT on that list, your activity will be sent without the URL information and will appear in RescueTime as an entity called "Other Web Sites".
Reason #1 is privacy. Some users or businesses don't want all of their web browsing data being sent to RescueTime, which is fine with us. If you really only care about how you use a few different web sites, whitelists are a great option.
Reason #2 is noise. The average RescueTime user visits 40 or more web sites per day, with many of them being new web sites. Having a list of hundreds of web sites (many of which were visited for 60 seconds or less) might be way more detail than you're interested in.
If you have a whitelist enabled, RescueTime will look for any match to the url in your browser's address bar. For example, if you added "google.com" to your Whitelist, RescueTime would send data for "www.google.com" AND "mail.google.com". If you added "www.google.com" to your Whitelist, it would send data for "www.google.com" but not "mail.google.com" (just like any other site that isn't on the Whitelist). Because many websites can use different 3rd level domains from time to time, we recommend not using the "www" unless you're sure that's what you want to do.
Your whitelist can be conveniently accessed on the privacy settings page.
If you're interested, you can add a "#" before any line to leave comments in your Whitelist.
google.com
yahoo.com
microsoft.com
youtube.com
facebook.com
wikipedia.org
ycombinator.com
rescuetime.com