Preferences

To open the Preferences dialog box, choose Edit > Preferences > [category name] (Windows) or After Effects > Preferences > [category name] (Mac OS).
To open the Preferences dialog box to the General category, press Ctrl+Alt+; (semicolon) (Windows) or Command+Option+; (Mac OS).
To restore default preference settings, hold Ctrl+Alt+Shift (Windows) or Command+Option+Shift (Mac OS) while the application is starting. To also restore default keyboard shortcuts, Alt-click (Windows) or Option-click (Mac OS) the OK button.

This section provides links to pages in which the various preferences that aren’t self-explanatory are explained in context.

General preferences

Levels Of Undo: Undo changes
Show Tool Tips: After Effects user interface tips
Create Layers At Composition Start Time: Layers overview
Switches Affect Nested Comps: About precomposing and nesting
Default Spatial Interpolation To Linear: About spatial and temporal keyframe interpolation
Preserve Constant Vertex Count When Editing Masks: Designate the first vertex for a Bezier path
Synchronize Time Of All Related Items: About precomposing and nesting
Expression Pick Whip Writes Compact English: Add, edit, and remove expressions
Create Split Layers Above Original Layer: Split a layer
Allow Scripts To Write Files And Access Network: Scripts
Enable JavaScript Debugger: After Effects scripting guide at the Adobe After Effects Developer Center on the Adobe website
Use System Color Picker: Select a color or edit a gradient
Create New Layers At Best Quality: Layer image quality and subpixel positioning
Preserve Clipboard Data For Other Applications: Importing from After Effects and Adobe Premiere Pro
Use System Shortcut Keys (Mac OS only): Keyboard shortcuts

Overflow Volumes, Segment Sequences At, Segment Movie Files At, and Audio Block Duration: Overflow volumes and segment settings

Enable Disk Cache and Maximum Disk Cache Size: RAM and disk caches
Conformed Media Cache and Clean Database & Cache: The media cache
Create Layer Markers From Footage XMP Metadata and Write XMP IDs To Files On Import: XMP metadata in After Effects

Output Device, Output Mode, Output Quality, Output During, and Scale And Letterbox Output To Fit Video Monitor: Preview on an external video monitor

Automatically Save Projects and Maximum Project Versions: Save and back up projects

RAM To Leave For Other Applications: Memory & Multiprocessing preferences
Render Multiple Frames Simultaneously, Minimum Allocation Per CPU, and CPUs To Leave For Other Applications: Memory & Multiprocessing preferences
Prevent DLL Address Space Fragmentation (Windows only): Memory & Multiprocessing preferences