Output_Buffering ??

Can someone explain output_buffering to me? I looked on php.net -- but cannot find reference to it -- it's a setting in the PHP.INI file. In my *production* .ini version, the output_buffering tag is set to 4096 (4k) -- what exactly is the intent of this tag? What brought this question up was when I upgraded from 4.1.1 to 4.2.1, and this time decided to use the production level .ini file -- when I ran a script from my command line -- no output was appearing -- that is, I have print() functions throughout my looping script -- and it wasn't outputting -- I set the output_buffering tag to equal 0 -- and my looping script now displays the text I want it to. Is it that when a script exits or terminates that this 4k buffer gets flushed out (in this case) to my screen? What additional processing occurs if this tag is set to off, or 0 (zero) ? Thanks Jason