They're very portable, so you can carry them around with you in case you come up with an idea of something to write on your Tesla while you're out and about. They stick to the surface quite well and don't wash off in the rain.

(Please try not to succumb to the temptation to write "F**k off Nazi Scum" or similar on somebody else's though like other people are suggesting. That might encourage people not to buy Teslas, which is a shame, because they're great American cars.)