If you already have the .net framework 4 installed, you do not need it.

No harm in getting the one with it. If you need it, it will install it from that package.

EDIT

It looks to just have .net 4 support, I do not even think you NEED it. Chances are you already have .net 4 installed anyway.

You can check in the add/remove programs to see if you have it or not. It was released last year, so good chance you have it already.
 
.NET framework is a just-in-time compiler for Common Intermediate Language - that's the language programs written with C#, visual basic and other .NET languages get compiled you. You will not be able to run those programs without the translator (.NET framework in this case) and as far as I know, catalyst suite is written in C#.
 

zdbc13

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AMD requires .net for it's control center. You can load the driver without it but if you want to use all the advanced features in control center you will need it. If you load the full driver package from AMD it will install it, I believe.