Sprinkler system – is blowing out the underground pipes necessary?

This is my first winter with a sprinkler system. I followed the steps provided by company who installed my system for winterizing:

1.) Drain the backflow from the above ground pipes, leave them partial open at 45 degrees, and cover the exposed pipes.

2.) Turn off the water at the underground switch that is near the street.

The company said blowing out the underground pipes isn’t necessary. I saw this morning that Space City Weather recommended draining sprinkler systems for the upcoming hard freeze, so now I’m a little concerned about that.

Anybody know?