What difference between DC mode and free-run mode in motor control?

I have an INVT EtherCAT servo that can operate in DC (Distributed Clock) mode or free-run mode. Could anyone explain the differences in performance between these two modes? Specifically, is DC mode more accurate than free-run mode in terms of reducing following error (ferror)?

I am not super familiar with ethercat, but I would think you'd want a shared glocal clock for all the servos if maximal accuracy of motion was your goal.

Yes, to have all servos/drives start acting on new data/position data at the same time.
For servos and drives you want distributed clock mode.

The following error in LinuxCNC with EtherCat is somewhat superficial.
If the drive offers a following error, use that, if possible.