MMS is most commonly used to send images with text. However, it supports other media types like modern chat apps, such as video, audio, contacts, etc.
Like SMS, it only requires a cellular connection with a mobile operator to deliver messages, which is a very optimal way of ensuring messages are being delivered to those without data or internet connectivity.
MMS sizes depend on carriers and the device. However, all operators reliably deliver MMS messages of up to 300 KB of data as a standard.