Upon another level, wild magic is the impetus that puts in motion all the forces of the universe. It is the soul of power that resides at the base of all things, the ghost in the machine, the atman, the means by which breathing powers the body. It is the magic that makes crops grow and seas rise, that topples mountains and cracks open the earth, that brings gravity and magnetism into existence, that causes the atomic foundation of matter to be orchestrated in the manner that it is. Wild magic is the thing that even the gods must take into account where it comes to the rules that define their limitations as well as those of mortals.
There is no reliable way to control wild magic. One method of perpetrating its existence is the discipline of occultism, which can have potentially disastrous consequences when invoked.
The reasons for my wanting there to be such a thing as wild magic should be obvious; it serves as a handwaving mechanism for all the absurdities and inconsistencies that exist in a D&D world. At the same time, as a DM, I do not invoke wild magic as a justification to do whatever I desire; it is an explanation for the weirdness of the world, and only that.