Why EXACTLY do we have sinuses?

Sorry for the weird topic but I am SICK of being SICK! Started out with a wicked sore throat and then moved north to my already bothersome sinuses. I have been coughing and blowing my nose like crazy. This is a great ab work-out by the way...

I feel like my head is full of solid cement. I was just wondering if anyone knew the purpose of having sinuses. So your appendix catches junk- and can be removed if necessary. Same with tonsils. Just kinda extra stuff we have right? But this is an actual empty space if you will, in our heads...

I think I will put them in my category that mosquitoes, acne, and childproof doorknob covers are in- pointless!

Okay, off to take too much cough medicine and eat some ice-cream...