The Mining Dimension has always been one of my favorite places to explore in modded games. A large part of this is that hostile mobs are generally prevented from spawning. This gives you some breathing room as you first get started in a new world.
But, while hostile mobs rarely spawn, passive mobs spawn frequently, creating herds of wild livestock that can provide food for hungry adventurers. Thanks to Pam's HarvestCraft, groves of maple trees also appear throughout the Mining Dimension, and between these trees and the local swine, you'll have easy access to maple cured ham, a very filling food that would soon become a staple.
However, all is not so quiet in this game. Tinker's Construct now creates floating islands fairly often, and these places are made from the slimiest dirt imaginable. The result of this is that hostile blue slimes spawn everywhere, even in the supposed safety of this dimension.