Originally posted by red13seto:

i wonder if it even saves time even with 100% chance of it exploding

No. It doesn't save any time.

If you just mine the exposed portion of a rock you get around half of what you get if you mine the whole thing (more if it's more exposed, on the side of a hill, etc). In my experience, it takes much more than twice the time to mine the whole rock, no matter how you do it.

As was mentioned, stone pillars and silver are a different story.