The Open Knowledge Foundation blog provides some excellent reasons to take open-source licenses seriously, especially for data on the Web, but these struck me hardest:
Together, a definition of openness, plus a set of conformant licenses, deliver clarity and simplicity. Not only is interoperability ensured, but people can know at a glance, and without having to go through a whole lot of legalese, what they are free to do...Thus, licensing and definitions are important, even though they are only a small part of the overall picture.
If we get them wrong, they will keep on getting in the way of everything else. If we get them right, we can stop worrying about them and focus our full energies on other things.
Efficiency can be reached through consistency and transparency. This is why licenses like the General Public License and Apache/Berkeley Software Distribution work in open source: everyone knows what they mean or, at least, what everyone else thinks they mean.
They're not perfect licenses, but they're understandable, and the Open Source Initiative has proved invaluable in ensuring the ongoing integrity of what "open source" means.
As the debate shifts from software to the data enabled and constrained by software, it will be critical that open data licenses emerge. Just as open source and open protocols paved the way for the modern Internet, so, too, will open data ensure the freedom of the next-generation Internet.
Open-source licensing is fundamentally about efficiency, not law. It's about understanding and keeping everyone on the same page so that the more important work can move forward. Licensing matters.