I would say that to really use OpenBSD as a desktop OS, the login.conf tweaks are non-optional. Otherwise you will find "big" software like browsers with more than a few tabs open, Office suites, etc. being killed due to the default memory limits.
Minor correction: firefox (at least) isn't "killed" due to memory limits. firefox segfaults because it tries to allocate memory and doesn't check for null. chrome in effect works around the memory limit by using one process per tab.
