What happens if we don't have eye brow?

You appear to own an enormous forehead, like that of Herman Munster.
Some idiots even tattoo eyebrows on, silly pluckers.

They keep sweat out of your eyes.

What @Seek_Kolinahr said – and they help us understand facial expressions.

They help you know if you’ve put too much lighter fluid into your barbecue

You would then need to try to make headbands come back into style.

Good luck with that.

Eye brows were originally to help keep stuff out of your eyes. They’ve become less and less useful. They do punctuate speech and even communicate without speech now. They may be accentuated to be attractive to others and in some cultures are used to mark membership in those cultures.

They serve as homes for little critters. They really do.

@janbb everything except your stove element (the part that grows red hot) serves as home for critters.

you do this http://www.muastore.co.uk/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/e/y/eyebrow-pencil-brunette.jpg

Buddhist monks shave their eyebrows (and their heads).