Expressions are great, but sometimes keyframes are better, such as when you want to manually adjust easing. Well, you can have your cake and eat it too! You can type or Pickwhip an expression, then convert it to keyframes. Just click the property name (the property to which you added the expression) in the Timeline and choose
Animation>Keyframe Assistants>Convert Expression to Keyframes. The good news is that After Effects will generate keyframes for your expression values. Even better news is that After Effects will not delete your expression. It will just disable your expression. To re-enable the expression, click the not-equal sign button next to the stopwatch. To delete keyframes, click the stopwatch.