The original purpose of this daemon was to route power management
requests to userspace, e.g. when the suspend button was pressed, the
APM driver posted an event read by apmd(8) that would invoke zzz(8) to
suspend. However, on ACPI systems this is all handled by devd(8)
events instead and running apmd(8) would just result in conflicting
event handling. This probably should have been axed when the APM
BIOS support was retired in commit 8c576a279ed5.