- It will disqualify your package from boarding an airplane unless you put the necessary stickers on the box (and sometimes the will not allow it, period).
- For international shipping, it will basically make a lot of customs agencies angry. The reason it is printed on paper is for reasonable permanence, doing this (assuming it passes the source country) will a) basically label that package as contraband and b) might talk to the source country on who the heck sent this and if they could file charges for endangering shipping (see lithium batteries warning above) or simply due to not following customs rules.
- It adds weight, which might matter (especially if your shipping rates is based on weight).
- Finally, even ignoring or mitigating everything on this list, your package could be simply handled so badly that the ink actually centrifuges away.