A quick fix for a messy address book
Duplicate contacts usually creep in from importing contacts from multiple sources -- an old phone backup, a synced email account, a manual entry. Running the merge tool every so often keeps your address book from quietly fragmenting.
It combines information rather than deleting it
Merging isn't destructive by default: phone numbers, emails, and notes from both entries typically get folded into the single surviving contact rather than one version simply overwriting the other.
Frequently Asked Questions
Can I lose information by merging?
No -- merging combines the phone numbers and emails from both entries into one contact rather than discarding either one.
Can I undo a merge I did by accident?
Right after merging you can usually click undo, but once time has passed you may need to manually split the information back apart.