systemd by default limits programs to a certain amount of memory (this bit me in the ass while working on getting OpenStack running on Ubuntu 16.04, and MySQL would get killed because of memory usage).

Various other systems also limit with things like /etc/login.conf on FreeBSD. There is also /etc/security/limits.conf on Linux for non-systemd stuff.

Limits for memory usage/open files/things of that nature are natural. You don't want one runaway process to cause the rest of your system to OOM.