Making it meaningful is key. Imposing an obligation without explaining the purpose it will serve or the results it will produce makes it harder for people to buy in and follow through. At least that's the case in France. Some even go to the trouble of doing things a different way simply because they didn't understand what the purpose was.
At the other end of the spectrum, limiting the approach to voluntary participation doesn't necessarily work either when it doesn't fit into a broader framework that makes clear the reason behind it and the importance of the measure from the government standpoint.
The fact of the matter is that the right balance is essential. The plan for 2020-25, which the General Commission for Sustainable Development is currently working on, balances the two elements. On the one hand, it sets out indicators for mandatory measures under the law, measures everyone has to comply with. There is no choice in the matter. On the other hand, stakeholders on the ground have the option to propose ideas specific to their context, ideas that would not have flowed from the central administration level. That's very important. When it comes to sustainable development, no one has the monopoly on good ideas.
Therefore, obligations need to be imposed from the top down, and good ideas need to be able to flow from the bottom up. It's a combination of both; success lies in achieving that alchemy.