Can you give examples of what this offers over, say, Google calendar? That already send to work fine for me, and has the benefit of syncing between all my devices.

Frankly, if you're happy with Google Calendar just use that. They really are very different, I'd compare remind more to working with the Google Calendar API.

You get to control remind with other tools if that suits you, but you also get to do the legwork to make all those integrations work. For my use case that includes birthday reminders generated from my abook¹ data, social reminders fetched and merged from a few different online sources, exercise reminders generated from goldencheetah² data, astronomy reminders generated with scripts over heavens-above.com, and more.

I find remind fits in to that category of tools where you make your own workflow that suits you, more than a simple tool you use. I've been using it since 2008, and my initial import was a code-assisted import from org-mode. I expect a similar transition could happen at some point in the future if I find another tool that fits my needs better.

FWIW, I have syncing across my devices but I'd sound like that infamous dropbox review if I suggested my way of working was for everyone. For example I'm happy with ical imports for visualising my calendar on my phone, and using termux for editing it when I don't have access to a real computer.

¹ http://abook.sourceforge.net/

² https://www.goldencheetah.org/

There's also calcurse, it's pretty simple but works great.