As you start doing things with Frictionless at some point, you'll have more items you have already done or can't start yet then items you can yet actually do.

This is where the Actionable Filter comes in. At the top of the Action Browser, you can switch between showing all actions (the default), and showing all actionable items. You can also select this using the filter pane. An actionable item is one that isn't done, isn't marked as an area, isn't marked as someday, isn't marked as a Template, and isn't before it start date.

Similarly, during your Daily or Weekly Review, you might wish to only view completed items, perhaps items completed the previous day or last week. There's a button and a filter for that as well.