This setting is typically used by the v6 client, and may be helpful to computers that are several years old. Big Work Units are typically larger in size in regard to upload size and RAM requirements. The Control Panel of the GUI-based v6 client offered an checkbox for these larger WUs. The command-line console v6 clients has “small”, “normal”, and “big” options which equate to expected file upload sizes of <5MB, 5-10MB, >5MB, respectively. This setting is not recommend for clients with dial-up modems, due to the large file sizes involved (and greater potential for transmission problems and WU loss). The availability of this class of WUs is based on the current projects that are running, so there is no guarantee the client will get these WUs.
All SMP WUs are hard coded to be considered Big WUs by the FAH client.