Air Admittance Valve Protective Cover - Is It Needed?

[BryceinSLC]

I just replaced an air admittance valve under the sink
The old one had the protective cover over it.
Is this needed? From what I gather its good for when its outside, but will having it on help or hinder when used inside?

Thanks!

 

[Terry]

I'm not aware of any reason for putting a cover over one under a sink.