On the other hand, it's nice to be able to take a no-reboot AMI of the machine you're futzing with, risk breaking it, then just re provision from that AMI if you fucked up. And if you're chasing three or four nines of uptime you do the same but provision a new instance and futz with that one while your working one keeps on keeping on. Even big instances are cheap enough by the hour that you can afford to run and extra one while testing potentially breaking changes.