Watching a private lesson with Eric Hemphill 6 years ago, my most most glaring mistake was having too much weight on the mat. Such weak displacement caused me to be both less heavy and less mobile. Not a good trade!
As a general rule I want as little on the mat as possible unless I have arms/frames killed or rear-mounted.
Moreover, positions that create pressure lock you in and set you up for offensive defense as you have to commit more energy to set them up. On the other hand, dynamic positions that keep you loose and off the mat make it easy to adjust while offering little countering opportunity, as well quicker disengagement.
Example from Henry Akins: