[whpalmer4]

If you have enough completed items, getting rid of them will definitely make it snappier.

I would suggest using the File->Move Old Data to Archive feature if there's any possibility you might want to look at the old data again. If you are really sure that you don't want the stuff any longer (or want to prune some of it before archiving the rest), you can bring up the view bar, go to projects mode, select Completed projects, and pick and choose from the projects in the sidebar for deletion. If you want to delete completed actions from ongoing projects, go to context mode, All Contexts, Group by Project, Sort by Project, Completed Actions, Any Duration, Any Flag State, and you should be able to see the candidates.