I use linux VMs for tons of things these days and for the very most part I usually avoid LLvm and set them up with a single disk partition with everything in it. Granted, if I need a special type of file system I will create a partition for it, possibly even creating a separate virtual disk, but for the most part I create a single partition for everything.
I've not really has a problem with this method, but the standanrd installs often advise partitons for /tmp /var/ /opt /usr and /home etc. and so I'm wondering if i'm missing something. I typically have tools that will tell me if I'm running out of space so I'm not worried about one partition filling up the whole disk. What need is there for all this extra partitioning or LLVM for that matter in a VM?