REST says that we shouldn’t have actions that change state be accessed by GET requests. GET requests should always be “safe”.
One reason why this is important is that web spiders will access any link that you have on your site that is a GET, because it shouldn’t break anything. If you had a link to “delete my whole database” accessible via a GET request, web spiders would happily click on that for you. But if they saw it needed to be a DELETE, they wouldn’t.