Why do I need a custom kernel? - OpenBSD -

Actually, you probably don’t.

A custom kernel is a kernel built with a configuration file other than the provided GENERIC configuration file. A custom kernel can be based on -release, -stable or -current code, just as a GENERIC kernel can be. While compiling your own GENERIC kernel is supported by the OpenBSD team, compiling your own custom kernel is not.

The standard OpenBSD kernel configuration (GENERIC) is designed to be suitable for most people. More people have broken their system by trying to tweak their kernel than have improved system operation. There are some people that believe that you must customize your kernel and system for optimum performance, but this is not true for OpenBSD. Only the most advanced and knowledgeable users with the most demanding applications need to worry about a customized kernel or system.