[Proj] crs definition with both +nadgrids and +towgs84 parameters

["SAEZ Laurent - CETE Méditerr./DI/ETER"]

Hi List,

Someone could tell me what appens if +nadgrids and +towgs84 are both 
used in a crs definition (e.g. in the EPSG file) ?
Which parameter is taken into account ?
Is the behavior the same in all tools (cs2cs, ogr utilities, gdal 
utilities, mapserver,PostGIS...)
I ask this because IGN puts both parameters in its IGNF catalog (French 
CRS).
I wonder if it is not preferable to specify only one.
My main problem is to be sure that the grid ntf_r93.gsb is used by 
MapServer for NTF to RGF93 transformations.

Regards

Laurent