What's the difference between cap deploy and cap deploy:migrations, and where do I hook in?

capistrano.txt

NB: deploy:symlink is deprecated, don't hook into it!
https://github.com/capistrano/capistrano/blob/master/lib/capistrano/recipes/deploy.rb

deploy:migrations
  update_code
   strategy.deploy!
   finalize_update
  migrate
  create_symlink  <-- hook in here
  restart  <-- or here

deploy
  update
    update_code
      strategy.deploy!
      finalize_update
    create_symlink
  restart