We don't have too many computers at Ray where we have the option of doing either set up. All of the computers in the lab (I think) only have ethernet connections. Most of the machines that have wireless cards end up on projector carts. I'm personally suspicious of wifi cards because I used a Dell GX 280 for many years that would only freeze up if it had the wifi adapter plugged in. 

It looks like this might be an issue with the prority of various network connections: 
http://superuser.com/questions/436256/can-i-choose-wifi-over-ethernet-lan
http://levynewsnetwork.wordpress.com/2011/12/01/windows-7-default-internet-connection-choice/

If the wifi is being picked even though it's slower, it might have been given a higher prority than the ethernet connection in another life. But since there's probably no reason that you'd need to switch between wifi and ethernet connections on the fly, disabling the wifi is easier. A good portion of the wireless cards at Ray are a particular type that Dell makes that are basically impossible to install into a new machine because you have to push the antenna through the opening in the back of the computer, so I don't think I've ever removed one unless the whole computer was dead.