Inflammation is a protective reactions involving immune cells, blood vessels, and chemical mediators in response to hazardous stimuli such as pathogens, damaged cells, or irritants. Inflammation serves to remove the original source of cell injury remove necrotic cells and tissues that have been harmed by both the initial inflammatory process and start the repair process for injured tissues.
Here are the examples of diseases involving inflammation:

The Five Cardinal Sign
Heat
Pain
Redness
Swelling
Loss of function
Since inflammation is a general reaction it is seen as an immunity mechanism as opposed to adaptive immunity which is tailored to each pathogen. A lack of inflammation could undermine an organisms ability to survive by allowing hazardous stimuli like germs to gradually destroy tissue. Excessive inflammation especially chronic inflammation has been linked to a number of illness including fever, periodontal disease, atherosclerosis and osteoarthritis.