Worked for a performance monitoring company for 10yrs and to get any reliable information on "what does this mean", you need to contact the vender - - Microsoft in this case.
The Resource Overview is purely subjective roll-up of atomic measurements over some period of time.
As I read the display shown, the designer of the summary is being extremely conservative and desires to leave some excess capacity available for growth. The problem is "What are the min/max points for normal" vs abnormal.
re Networking: TCP utilization will max-out at 70-75% due to the contention design.
re Disk: start the Task Manager and on the Performance Tab, click Show Resources. During any MS Update cycle you will see disk rates thru the roof (you can hear it as well as see the slow screen responsiveness from excessive I/O)
All those [+] verifications are again roll-ups of various status items that are undisclosed.