Not only do they protect the top of our fingers from damage but they actually help us use our fingers efficiently – I think without nails the ends of our fingers would be squishier than they are now and so it would be difficult to pick things up etc. This is just my best guess though.
What do the others think?
Did you know that animal claws are basically just another type of nail? Animal claws are very useful for lots of things (climbing, catching prey etc.)