These types of calibration setups are meant to find the relative positions of apriltags on the field. This can be useful for certain vision system implementations which rely on solving for the position of the robot using multiple tags. (LL’s Megatag1/2 and PV’s MultiTag-PNP) This is what WPIcal does.
While WPIcal can help in finding small errors in apriltag placement, it isn’t very useful without implementing good filters to make sure the robot is using the apriltags appropriately. Team 6328 discusses that here: FRC 6328 Mechanical Advantage 2024 Build Thread - #264 by jonahb55
Another thing to note is that it is important to verify the results of your WPIcal field calibration with a tape measure to make sure the results are correct.
Unfortunately, WPIcal is not a replacement for on-field robot calibration, due to the need to adjust camera exposure and other such settings based on your event’s lighting. It is also important to make sure your robot’s pose estimate is correct based on where it is on the field during the calibration period. This can save a lot of time when debugging problems at events if you can rule out your pose estimate being incorrect.