What does "mount namespace separation" in the app SuperSU do? The title pretty much says it all. What does  "mount namespace separation" in the app SuperSU do and how does it affect other apps?
From the man page for mount:


  A mount namespace is the set of filesystem mounts that are visible to a process.


It makes it so that the superuser has separate mount points visible to it from the rest of the system/apps.  I believe the intention is to prevent any issues when remounting partitions, such as remounting /system as read-write.  With this option enabled it should remain read-only to unprivileged apps.

It can, however, just break things more.  It made my SD card unusable in root apps: Internal and external SD storage inaccessible as root