I use it mostly for chicken cordon bleu or pot pies, all of which say "DO NOT HEAT IN MICROWAVE." But I am NOT heating up the oven and waiting an hour for one freak pot pie or piece of chicken to cook. NOPE. In the microwave pot pies take about 10 minutes, the chicken cordon bleu takes 5-6 minutes.
Also, smores. And stale cookies.
I do NOT use it for water, though, that's what the tea kettles are for. They're actually much faster than the microwave.