Usage Breakdown

[#1]

What is the purpose/reason for a list of a users broadband breakdown into a list such as Web,e-mail,Gaming,streaming etc ?
Everyone will have an allowance on what they use so if the total used can be displayed at any time why is it broken down further ? and how accurate is it ? for example I have sent and received a number of e-mails this month but looking at the breakdown list nothing is showing ?
None of this is a problem just curious 

[#2]

Well, it can give you an indication of whether your traffic is being correctly identified (& prioritised), without the use of a wireshark capture. Especially useful when you can't run wireshark on a device.
Also helpful for people to change their usage patterns if they regularly reach their monthly allowance.

[#3]

Or a rough and ready idea if your WiFi is being hacked when you see excessive traffic on a category you don't normally use much.