There are 2 types of biodegradable plastics that I'm aware of. One is made from plant starch, usually corn, the other is a petroleum plastic infused with micro organisms.
The plant starch plastic has the advantage of being non toxic and can be composted. However, it is made from a food crop, takes up lots of land and water and gas to grow. A lot of corn is genetically modified (which I personally think is a bad thing), it uses a lot of pesticides and herbicides to grow as well as synthetic fertilizers etc. So, in reality you may not be using less oil to make this product.
The petroleum bio plastic, has the advantage of breaking down quicker if it becomes litter. However it is still toxic, and made from oil.
In general we don't "need" to use single use or disposable plastics nearly as much as we do.