This question already has an answer here:
Linux user namespaces are special, as they play the role of the owner of the other namespaces.
Distributions (Debian, Ubuntu, Arch, ...) seem to ship with unprivileged user namespaces disabled.
For example, when podman is run as non-root user and unprivileged user namespaces are disabled, one gets a notice like this:
user namespaces are not enabled in /proc/sys/kernel/unprivileged_userns_clone
It is easy to enable unprivileged user namespaces.
In which context it would be safe to enable them?