Biomass is obviously CO2 neutral as long as it is replaced. The ratio between burned and used is of course important. Is 1:1 CO2 neutral? Probably not, due to losses and transport. Is 1:2, 1:3?
Apparently some of the plants also choose/have to incinerate vulcanized rubber (tires) to burn green/wet lumber.
Frankly, just using the documentary as my reference, this seems like an awful scheme and I can't fathom how subsidies and policy supported this technology.
If solar, wind, hydro, nuclear, and grid storage cover most of the need, then biomass can certainly pick up some slack. And I'm sure there are plenty of industries that generate biomass as waste -- lumber, farming, etc. That waste would decompose into CO2, we might as well get some energy from it, right?