What is "for old time's sake"

Usage examples of "for old time's sake".

Or maybe she just reminded you of Ling and, deep down, you felt like you wanted to have her for old time's sake.

I only let you stay here for old time's sake-you were supposed to be gone by now.

I wondered if they'd ever gone to bed together just for old time's sake.

He goes up and down the great stairway once, for old time's sake, remembering the night Glory took him here.

I volunteered to be here when I heard you were coming through, for old time's sake.