When done via the GS-EDRV, you get the benefit of the Ethernet I/O driver doing all the communications and your code utilizing a simple interface through a G EDrive structure. No ladder logic. "it just works".
If you do it via RS-485, you are responsible for writing all of the MRX and MWX instructions for all the various drive registers and managing where they all go and what they all mean.
The structure simplifies it greatly with structure members
.Direction
.OutputFrequency
.OutputCurrent
.RunCommand
.StatusMonitor1
.StatusMonitor2
et. al.
The Ethernet I/O driver manages all of that for you.