Well, when you need to switch the phase you know...
Like, you have a top and a bottom mic for a snare, then you need to
invert the phase of the bottom mic (because when the top skin moves away
from the top mic the bottom one moves towards the bottom mic)
I guess most preamps have a phase switch as well, but if you preamp doesn't,
that's what the switch in cubase is good for
Can be handy when dual micing cabs as well, by inverting one mic's phase, you
hear exactly that stuff that's canceled away when they're in phase...