I think it depends on both the total volume of must and the SG of the must. The larger the volume and the more sugar in the volume the larger the viable colony of yeast needs to be at pitching and you get a larger , healthier colony if you rehydrate correctly. Rehydrate with poor protocol and the size of the VIABLE colony will be far smaller than if you simply sprinkle the yeast on top. Bottom line, if you know what you are doing and why then you can make the better decision. If you really don't know what you are doing then even a good decision may be the wrong decision...