for US citizens as you said probably nothing as they probably don't know when you left, only your returns

but for Visa waiver/ Visa countries it shows everything (in/out) etc

The last time I was in the US (A couple of weeks ago in transit to HKG) the immigration officer spent (no exageration) no less than 5 minutes looking at his screen and punching keys back/forth looking at all my entries/departures

He was extremely interested in the last 4 times I was in the US as they all had been transits only (to Europe)