Bit OTT I grant you, but these analytics fanatics I’m listening to over here in SFO are pretty passionate about what they do.....
The premise behind segmentation with web analytics is around grouping customers based on their behaviour. Once you understand why they behave the way they do you can do something about it.
So if a whole bunch of people are coming from a certain site and bouncing (not going further into your site or buying anything) you can do some analysis, change your strategy for them and then watch their behaviour change over time.
Alternatively ring-fence users who are converting well. They may come from a particular keyword in organic search, so it might be an idea to test variations of that keyword to see how you rank organically. If you don’t rank well, then try those words through PPC and get more sales.
Knowing who your customers are and how they behave is crucial to online success. Your customers are not sheep, they don’t all follow the route through your site you think they should. They don't always come through your homepage either.
By segmenting those behaviours, and understanding why they do what they do, you have the information you need to take action.