We'd had a set of circular pyrex containers for years, and with these rectangular ones going on clearance, grabbed the opportunity to add a few more. Plastic storage containers are OK, but tend to break down over time, especially if you put anything oily in them. And plastic isn't microwavable. With these pyrex containers, I can bake something in the container, serve some, store it when it's cool, and then zap it the next day, without ever transferring most of it from the pan to a different storage container. And despite being a glass, the material is quite durable; I wouldn't recommend intentionally bashing it against a hard surface, but I did drop one of the round ones once, and it was fine.