Does it matter whether things are biodegradable or not?

Biodegradable does matter. First of all not everything that is biodegradable ends up in a landfill. Trash often finds its way to our water ways, neighborhoods, natural preserves, etc. so it is definitely important that that stuff be able to break down. Second, things in landfills do decompose but simply do so at a slower rate. The landfill situation is depressing but it's a situation that can eventually be resolved.