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?