Everyone seems to suggest using these covers to help prevent the outdoor pipes associated with the fixtures from freezing.  Although I believe that the insulation in these covers is not 100% effective (similar to MANY other things in our lives), having one of these covers significantly reduces the rate at which the outside part conducts cold, so it can tip the balance and protect your pipes from freezing.  I always say that it's better to be safe than sorry.  Lucky for the Vegas locals, you can get these covers at Star Nursery right now for only $20. 

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