Granted, access to those files is slow as dirt because of the Plan9 filesystem, and there are some weird bugs where a process sometimes loses access to $cwd if it's not a native wsl filesystem (also a Plan9 bug reported to MS over a year ago). But it's tolerable when interoperability is necessary.
It also facilitates using the same filesystem under multiple WSL instances.
Windows has a mechanism for sharing folders; the protocol is SMB (CIFS is a dialect of SMB). You mount the the target and destination folders on the same machine (doesn't matter which one mounts the other), and then copy the file locally on the machine where they're both mounted.
Oh, hey, there's the C drive in WSL! ;)
ln -s /mnt/c/Users/Somejerk/Documents ~/documents
Oh, man, a shared documents folder!
Granted, access to those files is slow as dirt because of the Plan9 filesystem, and there are some weird bugs where a process sometimes loses access to $cwd if it's not a native wsl filesystem (also a Plan9 bug reported to MS over a year ago). But it's tolerable when interoperability is necessary.
It also facilitates using the same filesystem under multiple WSL instances.