Recently I was on a project which was using Nintex Workflow 2013 and we needed to have the site collection feature activated, as well as the Nintex Workflow 2013 site feature on all of the sub sites within this particular site collection. Well this was an intranet site which was comprised of 50 sub sites which would all need to be enabled.
In order to use Nintex Workflow the site collection feature must be activated as well as the site feature for any sub site which wishes to use the Workflow Product. As much fun as manually clicking through 50+ sites and activating the feature would be, I found a script online and tweaked it a bit to be a bit more robust. Original script author Vadim Tabakman wrote the bulk of the script, my additions are noted in the script comments.