When you apply an effect to a clip, it is set to default values and is active for the duration of the clip. After you apply an effect, you can adjust its properties using the Applied Effects panel. You can make an effect start and stop at specific times, or adjust the values of the effect over time by using keyframes.
You can apply multiple effects to a clip, and you can apply the same effect numerous times to the same clip with different settings. Keep in mind, however, that the more effects you add, the more time it takes to render the final movie. If you decide an effect is not suitable for your project, you can easily delete it in the Applied Effects panel.