Well, if you're already into coding, then building from scratch is good practice. Using Wix or Squarespace, you're not going to get that practice and are limited to the tools they provide. I can semi-see how one might like to use something like Wix or Squarespace but as a developer my self, I prefer crafting from scratch for this reason, I like having the ultimate control on what tools I have available and how I use them.