An excellent explanation of why air to the roots of plants is so important.
When I first planted my present garden, a nurseryman planted all the trees and shrub. He took each out of its pot, stamped on it with his boot, turned the root ball and gave another stamp. I was horrified! He explained that it was necessary to break up the roots. I lost only one tree due to root death.
I read about this last year, and it sounded like a good idea. I plan on making many holed in my pots this year, before planting in them. Here's a 1.5 minute video that explains it: