This is quite a complex question to answer. Firstly we need to understand what the biodegradable plastics are. There are two main categories:
1.Bioplastics, which are made from natural materials like corn starch;
2.Biodegradable plastics that are made like regular plastics using petrochemicals that are engineered to break down quickly
The most common material used in bioplastics is Polylactide acid (PAL) produced out of corn kernels. It looks and behaves almost the same as polyethylene (PE) and polypropylene (PP). Production of it uses only a third of the energy required for traditional plastics. It is fully compostable.
Unlike bioplastics, biodegradable plastics are made of normal (petrochemical) plastics and don't always break down into harmless substances: sometimes they leave behind a toxic residue and that makes them generally (but not always) unsuitable for composting.
They may seem like the perfect solution but it is not that simple. Bioplastics for example, when they decompose on the landfill may still produce methane, which is a very powerful greenhouse gas. Because they look like PP and PE they may be easily mistaken with them and enter the traditional plastics' recycling stream which becomes contaminated. Also production of them requires the same resources as we need in agriculture: land, water, energy, pesticides etc. There is a huge risk of the food prices going up when farmers switch from growing food to bioplastics and biofuels. Also some bioplastic and biodegradable plastics require relatively high temperatures to decompose, which means it may take years for them to degrade.
In my opinion the volume of plastics we consume can't be replaced with the biodegradable options. We need to rethink our consumer behaviours, our addiction to packaging and convenience. They can be used as a last option but only reducing our use of any plastic is the best for the planet.