Writing your busy time into another calendar is one way to stay out of double bookings. Handing someone a link is the other, and Keeper.sh now publishes one that covers everything you have connected at once.
Copy it from the integrations page and subscribe to it anywhere that accepts a calendar URL — another calendar app, a scheduling tool, a colleague's client. What arrives is your busy time from every source combined, rather than one subscription per calendar and the job of keeping that list current.
The link carries availability, not detail. Someone reading it can see the hours you are unavailable without seeing what you are doing in them, which makes it something you can share outside the people who already have access to your calendars.
Read more about everything Keeper.sh does.