Advantages
- Displays total count of items in inventory, not just whatever partial stack is on the toolbar
- Works even if bots steal your last item
- Allows you to automate production of an item and place blueprints without picking it up yourself
- One item can have multiple bookmarks without getting confused as to which slot has the stack or wasting space with extra stacks
- Less total inventory space (but this can be compensated by increasing the main inventory)
- Less ability to subdivide stacks before ctrl-clicking them into something