I think it largely depends on the quality of care offered by both the gp and the consultant.
If the doc tells you that T2 should be treated entirely with tablets and to carry on life as normal, then i would be asking for a referral to a diabetes clinic!
But then, the consultant may do that too...
In theory, the consultant and registrars at the endocrinology or diabetes clinic will have vastly more experience on the subject, be up to date with the latest research, and be able to offer more treatment options. But this isn't always the case, and most T2s don't really need that quality of care. This forum has done far more for my control than my endocrinology appointments.
I have been seeing consultants and registrars annually for 15 years now, and I have to say that only 3 of those visits were worth the petrol. Pretty bad odds, eh?
But those 3 were so excellent that they made huge differences to my quality of life. Interestingly ALL of those great visits were with young registrars. The twice i have seen the head honcho Big Cheese Consultants, i left wanting to shoot them for their patronising arrogance.