I suppose it is a matter of preference. A friend was trying to email someone who is not in the Contact list. Check Names opened the Check Names window. Closing the window wiped the email address from the To line. That is not "a good thing".
I can see that Check Names has some use when an email address is similar to but not exactly what is in the Contact list and therefore probably in error. But there is no way Check Names can determine that a new address is in error --just because it is not in the Contact list.
Is there some way to turn Check Names off? I guess that is really what I should have asked in the first place. Sorry.