Software Testing types

Hi, when I was starting my career in s/w testing , the frequent question I faced was "how many types of s/w testing" . every time I had different answer. later once I was goggling I found a site named http://www.testinggeek.com/ . here I like the way in which they described the testing types. I loved it. hope you will find interesting this.
here the some useful matter which I am pointing based on the content provided in that site.

So the first question is this, why do we need to categories software testing into different types? What is benefit of this? Lets discuss.
As the purpose of testing is to find the defects in the software. So we can categorize these defects on different requirement and user expectation. For example
-> Functional defect-If system is not functioning properly
-> Performance defect-If system is not performing well
-> Usability defect- If system is not usable
-> Security defect-If system is not secure And so on...........

Now to identify these different types of defects we need different skill set, different techniques, different types of test cases. and to do this job we need to categorize our testing process.
So there many ways in which software testing can be categorized.

Based on knowledge of system :
1-Black Box Testing
2-White Box Testing
3-Gray Box Testing

Based on SDLC :
1-Unit Testing
2-Integration Testing
3-System Testing
4-User Acceptance Testing

Based on purpose :
1-Functional Testing
->Installation
->Regression
->Upgrade and backward compability testing
->Accessibility
->International and localization
->API

2- Non Functional Testing
->Performance, Load and Stress
->Usability
->Security

This is possible category. It may be exceeds.