Stream video at same bitrate as what they were converted?

[ksbigfoot1]

We are using ffmpeg to convert 3 videos at -b 1500k, -b 1200k, -b 800k. 

We are using the flash media server that uses a F4M config file to stream either a large, medium, small video

My question is should the videos be streamed back to user at bitrate 1500, 1200, 800?

Or does it matter that the bitrate to be streamed back to user is listed as 900, 600, 200?

[ksbigfoot1]

I found this link: http://www.adobe.com/devnet/adobe-media-server/articles/beginning-fms45-pt06.html

That shows to have the bitrates the same.  I am just wondering why.

Can anyone point me in the right direction to read up on this?