what are the benefits of the four signs of inflammation?

I'm guessing by four sign you mean swelling/fluid build-up, redness, heat etc. These are non specific defenses against pathogens. The heat makes a pathogen's reproduction cycles less effective, limiting the number present at the site of infection. The fluid build-up is caused by Mast cells and damaged white blood cells releasing a chemical signal that makes your capillaries 'leaky' (where the cells making up the capillary walls separate slightly). This releases plasma, more white blood cells and most importantly antigens. White blood cells and antigens fight infection, killing off any pathogens in the area. Inflammation is basically the body's way of dealing with infection.

This is what I've got from my A2 Level biology textbook, hope it helps! :)

So you can properly diagnose and treat it.