Well, no, they're never required. And as a rule of thumb, they're bad.
I can see why you might sometimes need it, but it should be a really really rare occasion and... Quite honestly, you should reconsider if it's really really necessary, or if you're just dumping a bunch of unnecessary information on the reader.
My personal rule of thumb is: "Don't show anything that the main character doesn't need to know."
Like, how the gods created the world doesn't matter if your main character just wants to learn how to throw a fireball, so don't bother with showing how the gods created the world. Your MC doesn't need this knowledge, so why does your reader need it?
And if your MC already knows how to throw a fireball, then you don't need to explain how it works. Just show the MC throwing a fireball. The MC already knows it anyways, so why should it be explained to the reader? What does the novel gain from the MC monologuing about something they already know how to do?