You can hide/show channels in the Mixer according to their type; for example, you can hide MIDI channels while working on instrument channels.
Prerequisite
The Mixer is shown, either in the lower zone or in the Mixer window.
Procedure
In the Mixer toolbar, activate/deactivate each channel type.
Result
Channels are shown in the Mixer when their type button is activated, and hidden when it is deactivated.