Business Insider reported on a study that found both messy and clean desk environments productive in their own way at their own time:
Messy desk at the beginning of a project, which is more conducive to brainstorming and creativity
Clean desk at the end of a project, which is more conducive to control and organization
As for me, the attainment of a clean desk is often a precondition to start something new and do great work. So, for today, it is clear and ready for another project.