Not all mushrooms will grow on straw but for those that do, using straw as a main substrate is a cheap, abundant, and relatively easy to use method.
In comparison to using sawdust blocks, the down side of using straw is that it's messy (straw will get everywhere!), risk of contamination is greater, and you are limited to the amount you can pasteurize in one sitting.
For these reasons many mushroom growers will favor wood sawdust blocks.
