@Indica_Jones,
The straw is to smother the cover crop, which will kill it off for the most part. I plant the cover crop so that it can at first work on nitrogen fixing (mostly beans and clover in the cover crop) and then I kill it off to feed the soil. I’ve got about 1,000 worms in the soil and the cover crop feeds them too. The straw also helps with moisture retention for the soil. Cheers!