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From the behavior I see on my system I am going to say it is looking for full signatures in emails that include phone #s and maybe addresses and emails. If it sees changed information then it pops up.
As far as new contacts it seems to look for the same. I have plenty of emails with no phone or email and that never pops up. Or with emails that have just a name and email address where I can get a drop down arrow but the line you have in your question does not come up.