Freeing normally: No problems when it does this.
Slipping: This will not affect gear changing but will result in increase in revs with no matching change in road speed as I am sure you are aware.
Dragging: This will make gear changing difficult, often create a "grinding" of gears when engaging and creating a jolt as first is engaged first and will often make gear changing heavy on the toes. When at rest it may also make the bike creep when in gear. As for neutrals a dragging clutch usually makes selection of the true neutral very difficult, rather that creating false ones.
So where does that lead us? Well in my experience it at least eliminates the clutch and takes us to the culprit.......the gearbox. The likely candidates are the selector forks, and the camplate if either/both are worn or the gear change quadrant assembly if worn or assembled wrongly. You will need to open up the gearbox, but if you have a manual it is easy to follow. HTH.