(setq-default
;; Defines the behaviour of Spacemacs when installing packages.
;; Possible values are `used-only', `used-but-keep-unused' and `all'.
;; `used-only' installs only explicitly used packages and deletes any unused
;; packages as well as their unused dependencies. `used-but-keep-unused'
;; installs only the used packages but won't delete unused ones. `all'
;; installs *all* packages supported by Spacemacs and never uninstalls them.
;; (default is `used-only')
dotspacemacs-install-packages 'used-but-keep-unused)