honestly, it depends on how you view warranties. I am a believer, and have them on both our 2010 silverado and 2012 tahoe. I would make sure they are GM protection plans, and not third party. Third party warranties tend to be a pain in the a$$, but not always. It will make a pricing difference if your Yukon was purchased as a certified preowned or not.
Choice is yours. I just had a heated seat malfunction in my pickup, to the tune or $750 for the repair...but warranty covered it.