Animation Preferences

In the Menu Bar, click Edit > Preferences, then on the left side of the dialog box, select Animation.

Base

Time - Set the number of frames rendered per second of animation.
Keep Keys at Current Frames - When selected, all keyframes remain in their global position, even when changing the global time. As a result, those curves are modified. When deactivated, keys may map to a different frame when the global time value is changed.
Verify Clip Structure - When selected, unreferenced animation blocks and empty clips are removed when importing a VRED file.
Don't show Create Curve Dialog - When selected, the Create Curve dialog no longer appears.

Playback Speed - Set the number of frames processed per second.
Playback Range - Select whether the full or detailed range is played.
Evaluation Context - Define which curves are calculated. When set to Scene, all active curves and blocks are examined. When set to Curve Editor, only the curves currently displayed in the Curve Editor are examined.
Loop - Toggle playback looping. For continuous looping of playback, toggle this on.