Our kids use most of the half pint jars that are always littering the kitchen, but I also use them to drink coffee and cocktails from time to time.
Microwave safe means you can heat up your beverage without removing the sleeve. Or take out a frozen jar of food, put a koozie on it, and heat it up.
Since they don’t touch your beverage, I often just rinse them, but they are also dishwasher safe. You can leave them on the jar, but I find that water gets trapped so I prefer to separate them to clean the jar.
You could also use one to block sunlight or prying eyes from the contents of your jar.
Great for kids and adults!