I like the ability to write iMessages from a laptop instead of getting my phone out, plus how Photos sync's up with my iMac, phone and whatever else. I can Facetime my mum when I'm cooking instead of having to balance up my phone on something. iCloud for Windows was terrible the last time I tried it. I'm also a UNIX/Linux admin so I like the ability to use terminal to do things as well as connect to my Debain server natively.
I use Windows 10 most days for my gaming rig (see sig) however that's only ever when I want to play a game. Everything else is done on my iMac.
Also printing, and this really annoys me, no matter what I do, I cannot print/scan using Windows 10 and my HP printer. iOS and macOS work first time, every time.
And don't get me started on Windows backups/restores!