Most cats are quite capable of grooming themselves but there are times (or breeds) when a helping hand may be required. This is especially true for long-haired cat breeds!
With an increasingly dirty and polluted environment, especially for outdoor cats, coat issues seem to be on the increase. Better care means that cats are living longer. This means they live to the point where arthritis or other medical issues can hinder their ability to self-groom.
So be it long hair, old age or other, expert cat grooming can keep your cats coat in best of shape.