I tend to work on both Open Source and Commercial software.

The cost of context switching between different tools because of it's licensing makes it a non-starter to use one for open source and the other for commercial work.

Granted, the cost of a tool is minuscule compared to the potential gains from speed of development, and any corporation that balks at paying for tools for their developers won't be in business very long, I still find myself penny pinching and using free and or open source tools, even if inferior or lacking in just one or two bits of functionality.