Effect Enabled button

When you create a keyframe for an effect, a stopwatch icon () appears in the Effect Enabled button next to the effect name in the Effect Controls palette. Once the stopwatch appears for a specific effect, Premiere automatically sets new keyframes whenever you move the edit line and change the effect's controls. Clicking the Effect Enabled button again, which removes the stopwatch, deletes all keyframes, except the default keyframes. Setting a value for an effect control when the stopwatch has been removed modifies the default (first and last) keyframes, and that value remains in effect for the duration of the clip.

Applying Effects > Working with keyframes > Effect Enabled button