You might wonder why? Put yourself in the shoes of a customer who has a smartphone and is driving. When he is searching for a dining service, the intent is to find the closest one to his location, ability to make reservations online, get driving direction or perhaps browse the menu quickly. If the same customer is searching for a dining service on a desktop, the intent might be different and may be geared towards finding one that offers delivery services, best rates, coupons and so on. Notice the intent is different and one should offer a different experience for mobile and desktop users. Hence a dedicated mobile website with a separate URL than the desktop.
If, however, you are riding NJ Transit and want to catch up on latest news, the intent is similar to what you would want doing the same on a desktop or a TV. In other words, the intent is to consume latest news and you would want to present the same content in the best possible format on that device, thus responsive web design.
Google supports both the configuration and does not bias one over the other.
Give us a call at 408.475.8050 or fill up the contact form and can review your business to recommend the best solution for success.