It started syncing and just couldn't stop.
I had to delete or move all the Backup and Sync contents across my devices to get to 0 before it quit endlessly thrashing.
Also its UI (IIRC written in Python) often fails to load (give you a blank box).
Dropbox is the best at crawling a very complex directory structure with millions of files and diffing it efficiently with the server and other clients, and then transferring all the individual changes. Nothing else comes close. And their write-ups show the work involved:
https://dropbox.tech/infrastructure/rewriting-the-heart-of-o...
https://dropbox.tech/infrastructure/-testing-our-new-sync-en...
But also throughput is good.
Their blog posts explain why they're so much better:
https://dropbox.tech/infrastructure/rewriting-the-heart-of-o...
https://dropbox.tech/infrastructure/-testing-our-new-sync-en...
"Backup and Sync" still misses features like Files On-Demand/Smart Sync available in OneDrive/Dropbox and deleting files online pollutes the local trash/recycle bin on macOS/Window computers.
"Drive File Stream" actually has these lazily loaded file placeholders, but it is treated like an additionally mounted volume instead of a local folder somewhere on my local disks. It also managed to occupy over 60 GiB RAM for over a week during its initial sync which had lots of small files created by Arq Backup.
It seems like 'unlimited' cloud storage is foremostly limited by the performance characteristics of their sync clients.