Showing one property at a time. A, P, R, S, T, and similar single letters isolate Anchor Point, Position, Rotation, Scale, or Opacity in the Timeline panel, and pressing the same letter twice (like TT or RR) reaches a related property.
Keyframes and easing. F9 applies Easy Ease to selected keyframes, and Alt+Left/Right (Option+Left/Right on Mac) nudges a keyframe by a frame at a time.
Masks and shapes. Single letters switch between mask combine modes (Add, Subtract, Intersect, and so on) while dragging, the same convention as the shape tools.
Numeric-keypad shortcuts. A meaningful share of the shortcut set, marker placement, paint tool opacity and flow, memory purge, lives on the numeric keypad rather than the main keyboard, and Mac often adds a Control-based alternate for keyboards without one.