Database Pivoting - what is the purpose?

Question

Why would someone want to convert columns into rows (ie pivoting)? Which problem does it solve?

I found some links, but did not get satisfactory answers to the quest

Answer 1

How about this as an example?

How to PIVOT Data Using T-SQL

A common expectation in data extraction is the ability to transform the output of multiple rows into multiple columns in a single row. SQL Server 2005/2008 provide the ability to do this with the PIVOT operator in a Query.

EDIT

Lets say you have a table that stores sales per customer by date

Something like

Table
- SaleDate
- CustomerID
- SaleAmount

Using PIVOT you can display a grid that totals sales per client by month/quarter/year

    |Client A|Client B|Client C
--------------------------------
2007| 100    | 0      | 150
2008| 0      | 200    | 160
2009| 110    | 180    | 100

This would purely be for summary purposes.