Ableton's Live walks through a fast, practical piano roll workflow for MIDI sequencing. After double-clicking into a clip slot to create a new MIDI clip, notes get added across multiple octaves to build out a musical idea.
Once the notes are in place, the Fold button collapses every unused pitch row, leaving only the notes you've actually sequenced visible in the piano roll. This clears out the visual clutter of a full keyboard grid, making it easier to see your melody or chord shapes at a glance and edit them without hunting through empty rows.