I can start writing an e-mail on my phone, put down my phone and then continue working on it on my tablet, and then putdown my tablet and immediately finish it up on my desktop in Linux?
Handover is more than a global clipboard.
I was doing that in the 1990s (thanks to IMAP and auto-saving drafts) without any vendor lock-in.
It is not huge, but it is the opposite of the thousands paper cuts. It’s a reliable features that provides thousands tiny time savings and some small convenience. It was not uncommon for me to send myself emails with URLs of things to have a look at when at home before this sort of things made switching devices much more convenient (Air Drop also helps immensely).
Now when Linux can do the same thing with a word processing document, with an IM client, with a spreadsheet, with a presentation program, with my web browser; let me use my phone as a webcam, a signature pad, or a document scanner, get back to me.
I've lived in the Apple ecosystem for a few years and Handoff/Continuity can do some impressive things (like the webcam thing of late, or cross device phone calls) that I ended up not using in practice. That's just me though. I prefer the simple way.
When Handoff or associated features don't work when they should, good luck troubleshooting.
Even if you save it as a draft, you'd still need a way to sync it between your devices. Handoff makes it simple and convenient.
I also have this same experience with Slack.
I often switch between mobile and Linux desktop for these applications, no special software required.