The only reason for filling the hub cavity with grease is to prevent ingress of water. But for that to happen requires two things;
Loose or missing hub seals and submergence of the axles in water.
It is a good idea to stuff them pretty full if you have plans to do any serious off-roading (that involves water deeper than your axles) or if the seals are shot - up to a point.
It is not uncommon for some hubs (Warn for example) to have binding problems (esp. with dis-engagement) due to excessive grease. The dis-engage spring behind the clutch assembly can't shift the clutch back out.
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If you do not intend to drive through streams and ponds a light coat of paste lubricant is all that is required.
Exerpted from Warn's maintainance manual:
Service Instructions
Service Kits are available. Hubs should be serviced at thesame interval as the wheel bearings. Remove in reverse order of Installation procedure(III). Then clean and lightly grease internal working surfaces. Do Not Pack theHubs with Grease, the Hubs will NOT Function Properly.
Maintenance
When new: Warn Hubs are assembled at the factorywith the proper amount of grease so an additional amount is not required. When servicing:A "light coat" of molylube #1 will suffice. (Note) Hubs should be servicedat the same manufacturers suggested intervals as the wheel bearings.I brush on a thin coat of Permatex Nickel Anti-seize and wet it down with WD-40. Never have a problem, the clutch and operator slide smoothly for years.
