Athletics and Acrobatics were the two most ridiculously easy skills to increase, often resulting in faster level gaining. So, starting with Oblivion at least, constantly running, swimming, jumping and falling could reslt in you being a higher level, and thus the eneemies would scale with you. But without increasing weapon, spell and armor skills at a similar rate, the enemies could possibly overpower you. I run and jump constantly, I don't need to level up simply by travelling from place to place.
Ever since Morrowind, I would usually take Custom classes, especially with the redunancy in the pre-generated classes. I don't need multiple armor types. I'm not going to be using every weapon type. Several skills are easy enough to increase even when they are Miscellaneous.
I'm sneaking constantly, but I dont need to invest perks in it, so I'm saving them for other trees, like Smithing or Enchanting. But I need to start using those skills some more, so I can qualify for the perks I want.