Usually, when people build remote mining bases, they build them in locations that are out of the way and therefore an unsound target for initial attacks.
Personally, I think the remote base is a major strategical advantage, as it allows you to allocate specific tasks to different areas (for example, you can save space in your main base by mining in a remote base and using metal storage in the main). Also, if you get a foothold outside your opponents bas, but don't quite have the firepower to burst through the defence, a vehicle base at the frontline can boost your army size.
However, the biggest advantage is the ability to hold on past the destruction of your main base. I had a 1v1 on one of the world maps in which I had a small mining base with a vehicle factory on it. My opponet decimated my main base, and just couldn't seem to spot the mining base.