In theory, it should keep the pinion in better alignment, and more accurate clutch engagement/disengagement. It remains to be seen. There are 30 year old Curado Bantams in use by tournament pros that have NO BEARING to support the pinion. It rides on the spool shaft.
No, the pinion rides on the spool shaft. The yoke pushes the pinion up the spool shaft when depressing the thumb bar. A bearing supported pinion should also influence less wear on the shaft when releasing the spool, but I don't think I ever ran across a worn out spool shaft either.
All that said, there's no denying smoothness of Daiwa's set up, or what SHimano calls X-ship.