We are talking about two different ways of representing data here.
Pivot chart: will do the grouping, will show the numbers, will give the sums but in order for the business user to figure out the "best selling product" for example, they need to go through and compare every singe value of the table.
Bar chart: A visual way to make it easier for the business user to do comparative analysis.
So the answer is: they might show the same data, but each object has a different usage. So it depends on what exactly you are trying to show and whether you want to emphasize on the actual values or the visual way of representing information.
The Designer's choice, if we want to be more precise, since the Designer is the one that needs to know the design best practices. :-)
Basically yes but each one with it's pros and cons.
You wouldn't use a bar chart if you had 100 products and want to show the Sales per Products.
(Unless you use the X-axis scroll bar for this of course)
So, it has to do with the business case, the designer preferences and, last but not least, the manager's or customer's preferences :-)
Don't forget that you can create a drill down group and use this in the bar chart, essentially creating something of a hybrid between the two. When there are too many dimensions to be displayed or understood then consider how you can either group them, sort them or highlight important points to make them easier to understand
Size and position are very easily interpreted by our brains so they are a good way of getting a quick summary of the data into somebody's head. However, if the precise number is important then a table of figures should be used.
i agree with agis ,
simply i can say i have 100 products and its amount .
when i go for dimenaion is product>expression is sum(amount) -- it is going to show 100 products sales in barchart.(imagine how bar chart looks for having 100 products amount) ,it can not clear ,not good to see.
so in this case we can go for pivot and all....
thats depends when u want show unlimited number of expressions and dimensions then we go for pivot instead of bar chart