I asked myself the simple question: "what is the purpose of tanks?", and I came up short.
It is said that a common misconception of tanks is that they are designed to destroy other tanks. That is definitely a role that tanks serve, but it does not seem to be a primary one as field guns and artillery can often do as good a job, and cost significantly less to produce.
Tanks are great at taking out fortified structures, but this seems to be a niche use of them. How often will a tank, in the course of its combat, actually encounter a pillbox or fort?
Tanks are excellent at combating infantry, but how realistic is it that tanks can make a significant impact on infantry regiments? When we talk about tanks, regardless of the threatre or time, we are talking in numbers of, at the very most, thousands. The Battle of Kursk in total only involved several thousand tanks (a record which afaik has never been surpassed), but 4.5 million men. Million. What impact can a few thousand tanks have on a couple of million soldiers?
So I ask the question: what is the purpose of tanks in warfare on a big scale? While tactically their importance is obvious, what strategic bearing do they have? Why may tanks, in particular, decide a theatre of operations?
Edit: The comments to this question haven't been great in general, by people who seem to be saying "isn't it duh obvious" without actually being able to answer the question. O.M's answer is adequate (not that this question is allowed have any more answers), but doesn't really address the issues of large scale warfare. I would delete this question if I could. When I've done enough research on the topic, at some future date, I might post a new question and answer it myself. Maybe.