If you enable this feature, you will have to put a data.ini in your client folder.
You can only load up to 10 total grf files with this option (0-9).
The read priority is 0 first to 9 last.
--------[ Example of data.ini ]---------
[data]
0=bdata.grf
1=adata.grf
2=sdata.grf
3=data.grf
----------------------------------------
If you only have 3 GRF files, you would only need to use: 0=first.grf, 1=second.grf, 2=last.grf