Give Users Permissions with Drush
If you are adding new modules to a site, one of the things that you will encounter is that you have to alter the permissions of the users on your site. This can be tedious if you don’t like clicking buttons in the UI. For instance, in this screen cast I have enabled the print module. I show you how to use role-add-perm to give the anonymous user and the authenticated user permissions to use the print module one site.
So let’s say that I have to do that for 20 sites. Without Drush, I would have to log in to 20 sites, click at least 40 checkboxes, and depending on how granular I want my print permissions to be, maybe even more. With drush role-add-perm and drush aliases this no longer has to be a problem. For homework, try it with a group of sites using drush aliases.