What do the 4-camerad-smartphones do?

Whats the use of 4 cameras? Why has it been 1 camera since 2008 and now it has to be 4 cameras???? Seriously.
Answers

AVDADDY

You may safely ignore any and all features that you do not wish to use.

SRΛSC

Several functions. 3D depth photos, wide angle, monochrome, optical zoom Depends on the phone in question.