There is some reasonably nice designer support in Visual Studio that I'd rather not have to roll for myself, and it's a framework supported by someone else rather than me, meaning someone fixes the architecture bugs and does the main testing, leaving me to test just my workflow. I mean, I could roll my own versions of GDI+ calls, but I'd rather not. Same goes for my own serialization framework, XML parser, or some other element of the .NET framework.
When it comes down to it, these things are provided as a toolkit. Whether you choose to use a tool or not depends entirely on the problem you're solving, the suitability of the tool, and the time and resources you have available to achieve the goal.
