Learn how to use Substance Painter and/or Mixer to combine and modify materials, so you're not just at the mercy of what the Megascans library contains, but it's perfectly fine to make use of the Megascans library.
Thanks a lot, I'm starting to get the idea now. I'm assuming since I wouldn't be working with Substance Designer that I am able to use materials I haven't made in my portfolio pieces, is that correct? If so, would that include Megascans?