Systemd security w/o User directive

So every systemd service whose unit file has no User directive runs as the root user. Are there any security implications of this? Should I not run untrusted code as a service w/o using User directive or does systemd have some sort of permission sandboxing even though the processes run as root?

Comments

[Peter Timoshevsky]

I guess no security measures are taken by default, as there is a bunch of things you can do to sandbox services the way you want.