Before Alfred 3.6, you'll find the Large Type preferences in Appearance > Options (bottom left) > Large Type.
Large Type is a handy feature that allows you to show text in large characters across your screen. You can use Cmd + L at any time to show the text or the result of your calculation, for example.
In the Appearance > Options > Large Type preferences, you can choose to show the text on a semi-transparent background, or fill the screen.
If you're using Large Type as part of a Workflow, you'll find more details on the Large Type Workflow Object page.