Here is another way to start matwork. Players start at opposite walls. They do a forward roll, and when they meet in the middle of the mat, they start matwork.
As I say in the video, this drill develops your kinesthetic sense.
As our dear friends at wikipedia can tell you,
Proprioception, the kinesthetic sense, provides the parietal cortex of the brain with information on the relative positions of the parts of the body.Hopefully, you can see how a well-developed kinesthetic sense can be a good thing for a judo player to have.