If you have a villages home which uses KWIKSET locks, that little slot allows you to change the key at anytime (insert the key) then the special pin into that slot (shown in red arrow) then inset any other key of that brand- remove the special pin and it's changed.

I did this so my northern home and my FL home now uses the same key.

No locksmith needed.

If it's a NEW home they will hand you extra keys and this special pin in an envelope.