With no PIN, there is really no major advantage. Steal a card, forge a signature.
The advantage is that you now have to steal a card, rather than just skimming the magstripe of one. The idea is that the chip ensures that you have the actual card, and the PIN (mostly) ensures that you are an authorized user of the card. In the US, with chip and signature, we don't have that second assurance, but having the first is better than nothing.