Why two drummers in a concert?

i can give you two reasons:

1) Technical. Many use more than 1 drummer to help create a "wall of sound" (A idea originally coined by Todd Rundgren)

2) If you had seen the Concerts that Genesis gave in the 1980's they had two drummers (Chester Thompson and Phil Collins). They did this because Phil had to do the singing duties along with some of the drumming. Also Santana not only used multiple drum kits but also up to six different percussion play at the same time(sept 1980 @ SDSU)

The Concerts For Bang.: this was a concert of many bands(mush like the No Nukes concerts) and speed of setup sometimes necessitated keeping multiple kits on the stage, and sometimes other bands would join in on jam sessions(on the Last waltz DVD there is an example of this)

The Dead

The Outlaws

The Almans

CDB

The used it for just that more percussion. You use cyncapy (sp ck don't have it)and two drummers can play off of each other.

hear right here dude. Bonham is the terrific. hear to him in "Dazed and at a loss for words" - "Rock N Roll" - "good situations undesirable situations" - "Black canine" - "Custard Pie" have self assurance me me, i admire Moon to, he's my 2d prominent drummer, so dont think of im hatin or something dude. yet cmon, its in comparison to comparing a steak to a mcdonalds cheeseburger. your going overboard. Bonham is #a million, then Moon at 2, Peart at 3