About Strongarm and features

Strongarm lets you override the values of variables, and works with features so that you can export the values of variables into your feature. There are a couple reasons that you may want to add variables to your exported feature. You may want to:

1) Capture configurations that you want included when the module is enabled. For instance, if you are creating a new module and need the variable 'abc' set to value 'xyz', you could export that variable into your feature. When the feature is enabled, the variable will be set.
2) Capture variables that change in development for deployment. For example, if you need to change the available search modules during a deployment to production, you could a) visit the admin section of the site and change it after your deployment, or b) export that variable ( search_active_modules ) to a feature and deploy the new code.

An extra benefit of managing variables in features is that configuration changes are not forgotten when a production or staging or other development site gets updated. All the sites will be consistent.

I hope that helps explain some possible use-cases for the two modules.