Rear speakers - what do they add?

[Andysu]

And here I am, thinking about adding 2 speakers to my 3.1 system. How many speakers are in your listening room?

i think its around 156 or is it 165 JBL speakers

 

[Artsfols]

i think its around 156 or is it 165 JBL speakers

Oh, it must be the 165.x system. I have never heard of a 156.x. Where x=number of subwoofers.