The valve stem..
You need the nut on it so that the tube dies not fall in on install of tire. Then the nut has no real purpose.
Now if the tube is not positioned right, the valve stem will tilt & indicate this and you can drop the air, break bead and correct.
Also when riding, if you do a lot of burnouts, or tire fit is less than ideal, tire could slip on the rim.. then the cocked stem will indicate this and you can correct it.
Tighten up your valvestem, and if tube fails from the above conditions, the first indicator will be when the valvestem gets torn out, or starts leaking..too late then..
So my theory is, if its in the right place, no tightened nut needed. i run a double nut about 1/4 inch above the rim.