any DJs on here? i have a few questions....

I have a home stereo setup that I'm pretty happy with (it's pretty solidly mid-fi, but i'm young and not particularly wealthy), but lately I've become interested in DJing, something a few of my friends do for fun - most of them have nights at local bars where they play garage rock, soul, psychedelic or even metal music.

Anyway, I know the basics, but I have a few questions about DJ cartridges - the first being why are the output levels so high? A lot of DJ-specific carts have outputs twice as high as the MM cart on my turntable. My other question is why "concorde"-style cartridges exist. Do they make cueing easier by giving you slightly more visibility?
1) To make the bass louder. It's used to match beats
2) It's easier to see the needle while cueing