why must boot in single mode.

[Supote Leelasupphakorn]

Hi all

   I'm using FreeBSD 4.[89] for a few years. So far I upgraded my release to 
security branch
by following the instructions in /usr/src/Makefile and after finished, my 
box is running fine.
Only one thing that I ignored - rebooting in single mode but because I am 
not at the box's
console.

   Could anyone clarify me why we have to (according to comment in 
/usr/src/Makefile)
reboot in single mode ? Is it necessary ?

TIA,
pjn