It is a lot easier to upgrade an OS on a Unix box with proper partitions separating things you want to persist across installs from the OS. Makes backups and backup restores easier as well. It’s also best to have swap space be a partition. Though these days probably doesn’t matter.

A modern Windows install has something like 4 partitions these days for the c drive. Ones labeled restore, c, and I have yet to care to figure out the other two. On boot though you see just c.