Why is the EM important?

It is important because it furnishes information about the composition, the temperature and maybe the mass or relative velocity of the body that emits or absorbs it.

Explanation:

a high pressure system is a dense air mass that is usually cooler and drier than the surrounding air. a low pressure system is a less dense air mass that is usually wetter and warmer than the surrounding air.

in general, areas that experience high atmospheric pressure also experience fair weather. low pressure systems can cause the formation of clouds and storms. air usually flows from areas of high pressure to areas of low pressure..

the entire statement is true and correct.  

there's no diagram, nothing is illustrated, and no question is asked.