What is the purpose of a market segmentation analysis?

The purpose of a market segmentation analysis is to
determine how a firm should split up, or segment, its overall
market.

When firms set out to do this, they are hoping to
be more effective in marketing their product to various parts of their customer base. 
The firm does a market segmentation analysis to try to determine what segments exist in
its market.  The firm is looking for discrete groups within that market that might
respond to different marketing strategies.  Once the market segmentation analysis
identifies these groups, the firm can tailor marketing strategies to the different needs
of the various groups.

The purpose of a market segmentation
analysis, then, is to find discrete groups in a market so that specific (and hopefully
more effective) marketing strategies can be devised for each
group.