This is comically small, in the long run of things, but I've been preparing to add a lot of places for venues/etc from a lot of indie artists and where they record and such, and I've noticed I (and others) have a tendency to accidentally add countries to addresses. I do this commonly where I copy an address to find more information about it and paste it in later and just forget to remove the country. 

Others, just don't read the style guidelines, causing bad data (intentionally or not) and more edits and checks to have to go through. 

The site already has a database of countries and it's uncommon for places to be named after countries as a whole, most places have their city in the title; I feel like a pop up box just saying "it looks like you might have left the country in" (as happens already with strange looking UPC/barcodes), could just prevent this and aid in data going through clean and sorted rather than needing to be edited, or an editor missing a bad data edit they made previously and forgetting about it. 

I do think this is probably way smaller than some of the other things mentioned, like trying to prevent preserved link removal and etc, but at the end of the day it is something that creates more work over time as well.