According to Adobe, "To help with accurately setting values, the History & Cache section of the Performance panel in the Preferences dialog box now contains three buttons to help match settings with your work environment. The values set by these buttons will vary depending on the amount of RAM and number of processors in your computer. Click the option that best fits your workflow to set both Level and Tile settings."
Tall and Thin—Best for users working with images with smaller document dimensions and many editing and enhancement layers.
Default—Designed for general use when a user will be working with a variety of document types. This is the default setting.
Big and Flat—Works well with large images and few editing or enhancement layers.