Over exposing color negative film usually helps to ensure that your shadows have some detail in them. But to be totally honest I have better luck from exposing for the shadows to start with.

But, try it for yourself. Load your camera up with a roll of your favorite color film, shoot it at box speed. Then load the same film, shoot it one stop over exposed. Have it developed and see if you can tell any difference. I will bet that you can't. My experience is that unless you develop your own film, you won't see much difference.

Unless you are shooting Ektar 100 of course. The do yourself a favor and get your exposure right. This film does not like under exposure.