Granites used for benchtops can vary, not only in appearance but also in their mineral composition. They also have varying degrees of porosity or absorbency.
If the granite can absorb spills it needs to be sealed. However when the density is such that it won't absorb any liquid or even minute amounts, then sealing technically becomes impossible.
Applying a sealer to a granite benchtop that literally will not accept a sealer means that you will most likely end up with a residue on the surface. This will dull the surface and as it becomes dirty with soiling sticking to the residue, eventually the shine or lustre of the benchtop will deteriorate.
At this point most will say that their benchtop needs re-polishing or re-sealing to restore it. In actual fact the shine is possibly still there but hidden under the sealer residue.
Regal Floors are accredited sealer applicators and generally advise clients to seal stone surfaces. However, Regal Floors also advises when not to sealstone surfaces.