If you think you might want to access certain photos from Organizer at some point, but you don't want to see them all the time, you can tag them with the special "Hidden" tag. This keeps them in your catalog, but you never see them unless you specifically ask for them.
I use the hidden tag often for pictures that other people have sent me. I want them in my catalog, but they're not my personal photos, so I don't want to see most of them during everyday browsing of my catalog. By tagging those I don't wish to see as "Hidden" I can show them anytime by clicking in the find check box next to the Hidden tag.
Bonus Tip: When you do want to permanently remove photos from the catalog and the hard disk, it can be annoying to constantly click the "also delete from hard disk" checkbox. To save yourself the trouble, create a "Delete" tag and tag these photos as you are browsing. Later, when you have several photos tagged for deletion, you can select them all at once and then you only have to check the "also delete from hard disk" checkbox once.

