Notes are helpful in multiple scenarios. You can leverage them to document site conditions, communicate with your team, log service issues, export autonomously generated site reports, gather data on your portfolio properties, etc.
To name a few of the specific use cases are:
Flower bed installation requirements as notes
Subcontractor ticketing
Enhancements proposal for clients
The site walks with the client (bid walks, audits, etc.)
Service issue reporting by clients
Site inventory and customer requests