Show Edit History for Google Sheets
Google Sheets has a new feature (for some).
June 11th, 2019 Google began to roll out the new Show Edit History to Sheets. For most uses the service should be available within 15 days of the release date.
The Show Edit History tool is a right click away.
Locate the cell > Right Click > Click on Show Edit History.
The new Show Edit History panel includes the timestamp of when the change was made, what the prior value was, and who made the change (alone with the profile photo).