See Also: Fixed Members
For most applications, you should not use this container! It keeps you from having to learn about the other Gtk# containers, but it results in broken applications. With Gtk.Fixed, the following things will result in truncated text, overlapping widgets, and other display bugs:
In addition, the fixed widget can not properly be mirrored in right-to-left languages such as Hebrew and Arabic. i.e. normally Gtk# will flip the interface to put labels to the right of the thing they label, but it can not do that with Gtk.Fixed. So your application will not be usable in right-to-left languages.
Finally, fixed positioning makes it kind of annoying to add/remove GUI elements, since you have to reposition all the other elements. This is a long-term maintenance problem for your application.
If you know none of these things are an issue for your application, and prefer the simplicity of Gtk.Fixed, by all means use the widget. But you should be aware of the tradeoffs.