Tire truing?

I took my truck in today to get my tires balanced. I have had a shimmy from 45-55 mph since my last rotation. While they were at it, they trued my tires. Basically they shaved the tires in order to make them perfectly round. My truck didn't even drive this smooth when the tires had zero miles on them. Has anyone else had this done before and is there a downside to having this done to your tires?

 

So they shaved part of the tread off?? how did they do this? I thought that was the purpose of doing the tire rotation but it sorta makes since to start fresh if the tire has formed some big wear spots. What size tire are you running??

 

https://m.youtube.com/watch?v=8UxfakpQyMY

Here's a link of how they can do it. They did all of mine while the tires were still mounted. I'm running 35's with 17,000 miles on them.