If you change phones/tablets frequently you may notice some discrepancies in your location history.
I personally allow Google to keep my location history, but I want it to be on my primary cell phone only. Not on my backup phone, tablet or any other device.
To see a list of all devices associated with your Google account and select which one (or which ones) participate in location tracking, go to Google Activity Controls.
This page gives you a decent amount of control over your location history and devices.