I regard it as a major error to see evil as a tool wielded by God to bring about greater understanding and development. This is a fairly common trope, whether as a Christian heresy, a variation on Eastern monism or an example of the sort of Western occultism that seeks to present itself as more 'advanced' than religion for the unenlightened masses. But it is wrong.
Roughly speaking, the theory goes that without darkness you could not know light so certain angels act on behalf of God as forces of darkness and contraction. They do what we, in our short-sightedness, call evil but they are working for the spread of good. Lucifer, of course, means Light Bearer and, according to this idea, that is what he still is. He is the force that brings about individuality and breaks down spiritual inertia so that new growth may arise. He is sometimes even thought of as Christ's dark twin, the two working in tandem to bring about spiritual evolution as the One splits into the Many before recombining as the One.
I think this is pernicious nonsense. Tolkien (as usual) had it right. In his creation myth, the One God teaches the archangels who are the children of his thought to sing creation into being which they proceed to do along the harmonious guidelines laid down by God. But they have a certain amount of freedom too and one archangel brings in discordant elements, the product of his incipient egotism. Several times God corrects this by introducing new themes that balance it out but it seems that the end product, Earth, is still somewhat corrupted. Evil has come through the pride of the rebellious archangel and though God can use that evil to bring about some new good, the evil is certainly not the source of the good or the necessary means for it. It's more a matter of making a virtue out of necessity. Evil here is not a form of good but a perversion of it.
It is important to see this correctly or you can fall into the trap of justifying evil and not standing against it as the enemy of good rather than its accomplice. And that means you will become an apologist for evil or even an enabler of it. This is the philosophy of people who eschew divine simplicity in favour of over-elaborate cosmologies that appeal to the intellect. It can be dispelled by a proper understanding of Christ who leaves us in doubt that evil is not good. It is evil.