The main feature of Spacemacs over just plain evil is that it has a number of "layers" for different languages, utilities and emacs things, which introduce cons

The main feature of Spacemacs over just plain evil is that it has a number of "layers" for different languages, utilities and emacs things, which introduce consistent, vim-friendly keybindings. With plain evil-mode, you'd have to tinker with every package you wanted to use and come up with some good vim-style keybindings. The Spacemacs layer setup does restrict you to what it supports, unless you want to do things manually.