Sim City 2000 and Death Star jokes aside, I assume in real life it would be trivially easy to avoid accidents by shutting down the beam if it goes off target and it would be fairly ineffective as a weapon, since it would be a very expensive sitting duck that could never get off more than one shot.

If it could be made to work it would be very useful, but quite challenging technically.

Also someone will complain about the occasional bird getting fried, like they do with wind power.