* To connect to multiple devices. MIDI ports allow you to connect your musical keyboard to other MIDI devices, such as synthesizers, sound modules, and computers. Having two MIDI ports allows you to connect to multiple devices at the same time, which can give you more flexibility in your music production.
* To separate MIDI input and output. Some MIDI devices have separate input and output ports, which allows you to control the device with one port and receive data from it through the other port. This can be useful for connecting to older MIDI devices that don't have a single MIDI port.
* For redundancy. Having two MIDI ports can provide redundancy in case one of the ports fails. This can be important if you're using your musical keyboard in a live performance or other critical situation.