Edge blacken primary?

Is there any real advantage or disadvantage to edge blacken a primary mirror? Of course I've seen secondaries done, but can't recall seeing mention of anyone doing the primary.

Yes. Black sharpie. Also baffle it with some roughened black Kydex or ASB.

A word of caution, if you use a Sharpie or other marker type pen, never use alcohol on the mirror or the ink will migrate over the mirror and is very hard to get off completely. A serious mess of blue haze will take repeated cleaning with alcohol or acetone before you get it clean.
I think that one could use black tape and get the same results, but I am not sure that there is any real gains to blackening the sides of the mirror.
A baffle could be of some use, but I doubt that there is a lot of light requiring this inside a mirror box if properly blackened.

Mirrors eventually have to be recoated, and that means anything you put on, paint, ink, glue, needs to be cleaned off. I would hesitate putting anything "permanent" on a mirror.

IMHO the only reason to do this, is to eliminate turn-edge
effects and diffraction from mirror clips, etc. The stray
light from the mirror edge bevel is not worth worrying about.

As other people have stated, I would not put anything on the
mirror itself -- been there and done that -- its a big mess
next time you wash the mirror. Make some circular aperture stop
and place it couple inches above the mirror, if you must.
Try to allow air to circulate outside the stop, so rising tube
currents are not forced into the light path.

Thanks All, for your replies. The cleaning issue could be avoided by using only mild soap and water, I guess. And I suppose flocking could be used but that may cause a problem at recoating time. Seems that a baffle would be the best way to go then.
How important would it be to be knife edge sharp and perfectly round though?

Tim Abbott said:

Is there any real advantage or disadvantage to edge blacken a primary mirror? Of course I've seen secondaries done, but can't recall seeing mention of anyone doing the primary.

There is no reason to do this for any first surface mirror.