Editing the Estimated Hrs Remaining is a manual way of recording how much time you estimate the task will take. This is a great way to communicate that the time it will take for the task to be completed may be different to the Allocated Hrs Remaining. For example if you have 1 hour of Allocated Hrs Remaining, but an Estimated Hrs Remaining of 3, This would indicate that the task is going to go over budget by 2 hours. In reverse you may have 5 hrs allocated, but it may only take 2 hrs, so you would have an Estimated Hrs Remaining of 2.
Estimate Hrs Remaining is not synced to WFM and does not apply to other instances of the task.