Why PNG not JPG ? (Flash-Matic,u'd be the right person to ask)

Hi !!

Other day I was talking about using PhotoShop creations in Flash…

I wanna use PhotoShop graphics in Flash since PhotoShop fot lots of nice plugins which make ur work look awesome…

The member “Flash-Matic” told me its a good idea to do that… but he said : Use PNG format…

I was just wondering, why use PNG not JPG ?

Thanks