I have been able to summon assistance in areas where I had no cell reception, and I have used it for diagnostics issues (check engine light). Push a button and ask what the issue is and they will identify the problem and tell you if it is safe to keep on driving. They will even put you in touch with the nearest GM dealer, if required. The other advantages of having ONSTAR have been well documents above, so I won't try to sell you on it, other than to say I have it on two vehicles and plan to keep it.