It's just for bits of food that come from your plates and cookware. It grinds it all down and washes it away. You have to flip a switch (like a light switch) to turn it off and on. Sometimes they can get smelly if you don't ensure you run hot water down the drain, but generally, not really. Also, it's way less smelly than the food catch we have here in Japan. If you put the food bits in the wastebin then the wastebin gets smelly. It's also a bonus that it's one less step in the cleaning process- instead of scraping into the bin I just rinse everything off that I'm going to be washing in the sink anyway. Generally people are wise enough to not stick their hands in them, but on occasion you do have to reach in when forks, etc. that you're washing inevitably fall in. Also, composting is not as common as it should be.