Inflammation is an essential part of our survival package. From an evolutionary perspective, the biggest killer of Homo Sapiens has been infection, with cholera claiming a third of all deaths, ever. The body has to be alert to the possibility of any infection, to all of which it responds with inflammation. However, inflammation is metabolically expensive and inherently destructive. It has to be, in order to kill infections by bacteria, viruses, parasites or whatever. For example, part of the immune defence involves a "scorched earth" policy - tissue immediately around an area of infection is destroyed so there is nothing for the invader to parasitise. The mechanism by which the immune system kills these infections is by firing free radicals at it. However, if it fires too many free radicals, then this "friendly fire" will damage itself. Therefore, for inflammation to be effective it must be switched on, targeted, localised and then switched off. This entails extremely complex immune responses; clearly, there is great potential for things to go wrong.
Inflammation is also involved in the healing process. Where there is damage by trauma, there will be dead cells. Inflammation is necessary to clear away these dead cells and lay down new tissues.
Inflammation is characterised by heat and redness (heat alone is antiseptic), combined with swelling, pain and loss of function which immobilises the area being attacked by the immune system. This is necessary because physical movement will tend to massage the infection to other sites.
If one looks at life from the point of view of the immune system, it has a very difficult balancing act to manage. Too little reaction and we die from infection; too much reaction is metabolically expensive and damaging. If switched on inappropriately, the immune system has the power to kill us within seconds - an example of this being anaphylaxis.