Marcin Wichary:

By default, on a Mac, the initial delay is 500ms, and the key repeat rate 1000ms.

[…]

My suggestion is to make them both as short as possible for testing.

[…]

First, it’s good to test whether your keystrokes behave well when repeated. Occasionally you might want your interface to suppress repeating, or do something special if the key is held longer.

Second, it’s a good test not just of repeating, but just the user pressing keys really fast.

Previously:

• Testing Tip: Always Show Scrollbars

Esoteric Preferences Keyboard Mac Optimization Programming Testing