A small detail about Time Machine I hadn’t thought about before: this article recommends removing all the virtual disks from virtual machines like VMWare, Virtual Box, et al. from the backup.

Makes sense: Time Machine works at a file level, in the end it’s just something like this but with an über-posh interface. So every time you boot one of your VMs, some small change will inevitably be made on some file inside it, causing Time Machine to store a new copy of the full virtual disk.