What good is it to have a midi keyboard with multiple outputs?

I have a Roland A-70 which gives these details on the product website:

http://www.rolandus.com/products/productdetails.php?ProductId=446
-76-note "organ-touch" weighted, velocity- and channel aftertouch-sensitive MIDI Master Controller
-Highly acclaimed MIDI control functions borrowed from A-90
-Selectable velocity curves let users maximize the dynamics of their music and playing style
*************-Four independent MIDI OUTs control up to 64 MIDI channels; independent control for eight zones (4 external and 4 internal, or 8 external sound source zones)*************
-20 onboard controllers include aftertouch, bender/modulation lever & wheels and sliders
*******-Dedicated Sequencer Control section*********
-Internal sounds can be added as desired via Roland Voice Expansion boards
******-Provides very affordable MIDI master control*******
-Note that this product is no longer in production. Similar capabilities can be found in the A-37 MIDI Keyboard Controller.

So what do each of these highlighted things mean?? What good is having 4 midi outs? Thanks! I use midi at home with protools and reason, and want to bring it on stage.... I just want to know what sort of real life applications this machine is capable of.... Its hard finding info for this keyboard!