This is a 15 minute video on Dynamic Topology. It shows the difference in how we work with and without it.
This tool can be used for adding AND REMOVING polygons.
This tutorial also shows using the Symmetry tool that is part of dynamic topology.
Once you see the tool in action, you’ll understand how handy it will be.
(There is a bug in the current Chrome Developer. The URL does not always update. It depends on how you move from page to page. On YouTube the URL sometimes fails to update. I’ve been able to reproduce the failure, but not consistently. So, I got the wrong YouTube ID for the original posting and didn’t preview the post. It was short. Sorry.)