I won't lie to you - it's motherfudging disgusting stuff. Who in the hell VIDEOS that shizzle?! I've been vaguely with it for all three of mine and a birth partner for when my niece was born and I'm not sure which was the more horrendous experience. Sure, giving birth is a little on the uncomfortable side and with Jake I punched a wall because they wouldn't give me painkillers (ladies, do not do this. It hurts more than labour once you realise what you've done), but watching my sister give birth was just...gross. And the SMELL! Not to mention the involuntary peeing, pooping, farting, vomiting and other unpleasantness they don't prepare you for in antenatal classes (which are a joke in themselves). Seriously, stay at the head end, don't look down if you EVER want sex again (or even a steak dinner) and do not open your mouth unless you are ready to lose your teeth. Nothing enrages a woman in labour more than having her moron of a partner stroking her hair and saying dumb things like, "You can do it. Come on now. Nearly there. I love you." in a patronising tone. Little tip: your missus doesn't love anyone right now and she sure as hell hates you with a passion.
tl;dr - don't look, keep your gob shut and do the hell as you're told. It's better that way, trust me.