It is important to monitor and manage Earth's resources because:
By monitoring and managing the resources, we can keep track of what resources are increasing, decreasing, and so on. From this we can determine whether a resource usage needs to be restricted or what changes can be made to best preserve it while still being able to use the resource.
Here is a simple comparison example- Some animal species are monitored and some times even protected to ensure they do not become extinct.
Here is a simple comparison- In history a war called for more of Metal A to create bullets for guns, helmets, and such for our service members fighting the war. That being said, many every day items that were created with Metal A were then replaced with a different type of metal (Let's use Metal B as an example). This means the every day production of items that were made with Metal A were now being created with Metal B so that all of the Metal A resources could be put into the production of war accessories. (As previously mentioned: guns, helmets, shields, wires, etc.)