There's a similar question out there, but it's for Windows and the answer is not applicable. Right now, the minimum Skype window size on a Mac is about 2/5ths of my screen. That's a lot of real estate for just one conversation; however, Skype will not allow me to make it smaller. It's pretty irritating. How can I fix this?
The best you can do is drag the sidebar all the way to the left so it disappears. Then, the minimum size of a Skype window will be around 652×548 px.
You also can't edit Skype's interface files because Skype somehow checks the files for integrity and once you modify them, well …