It's not that free scan gives better detail, it allows you to move the object yourself to fill holes in the scan, and will make a better complete scan.

The calibration part (I think) is to calibrate the scanner with the turn table, so the software knows exactly where the model is, for aligning scans with the steps of rotation,
this will make a faster scan, but could leave hidden parts of the object out of the scan.

While I'm doing free scans, I keep an eye out for the cross that is projected on the object, and adjust so it is not to close or far away from the scanner,
in theory, when the cross hair is sharpest it should scan best, but certain parts of the object will always be closer or further away.
I don't see less detail on the resulting scan when the line pattern, on the object during scanning, is not sharpest.

I am really amazed of the detail of the scans, and auto aligning works great.