Setting up and using Apple's new Photos app is easy enough, but one thing you might not notice immediately is the ability to keep multiple libraries on your computer. Cult of Mac points to a keyboard shortcut that makes it easy to swap between libraries.
Whether you're sharing Photos on your computer with someone else, or you just prefer to keep specific photos out of your default library, having multiple libraries is handy. To set one up, just hold down the Option key when you click on the Photos app. When the Choose Library dialogue box pop up, select "Create New..." From then on, you can swap between libraries by holding down the Option key when you launch the app.