You can, but you shouldn’t. Those home improvement websites like Sick appliances will probably tell you the same thing. The grounds don’t have much influence on the machine per se, but they affects the drains, just like how you shouldn’t put eggshells in garbage disposals. After a while, you’d find out that they couldn’t be carried by the water all the way through. Instead, they’d end up in the P-trap, start building up and eventually clog the pipes.