Graphs like these are useful though not ideal because they take second-by-second data directly from your power meter, so it's ultra-precise.  

While they give you an exact plot of your power, they don't account very well for the variances inside of an effort. 

For example, a threshold effort will see some power numbers in your active recovery zone and others in your anaerobic capacity zone.  While it all adds up to a "threshold effort", the actual numbers that make up that effort vary considerably. 

So, in a nutshell, it's useful data but because of its extreme precision, may not "look" entirely accurate because of the constant (normal) variability.