Used to dismiss a correction to one's adherence to an alternative standard.
A: Then you hook the hose up to the bibcock, and you're done. B: You mean the sillcock. A: Tomayto, tomahto.
Used to dismissively suggest that a particular distinction is a distinction without a difference; used to express the assertion that two similar things are effectively the same, despite any trivial difference.
A: Then you revise the database record for that transaction, and you're done. B: You mean you replace the old record with a new one. A: Tomayto, tomahto.