They are basically the same. But you can sort of make it work the way you want. Here's what I mean by that. Every time you write something, you have 3 options. 1) Email it to your followers and publish on Substack. 2) Just email, but don't post on Substack. 3) Post on Substack, but don't email. Most people use #1 almost exclusively. But you don't have to.