Additionality is a crucial component of carbon offset creation because if it is not additional, a carbon offset does not reduce greenhouse gas (GHG) emissions.
Emissions reductions by carbon offset credits are considered additional if they only happen because there's a market for offset credits. In other words, if these reductions would not occur without the possibility of selling carbon offset credits, they are considered additional. This concept is crucial for the effectiveness of carbon offset credits. If the reductions would have happened anyway, without the option to create and sell carbon offset credits, then they are not truly reducing emissions on the electricity grid.
So, it is important that offset credits contribute to real, additional greenhouse gas reductions to make a positive impact on the electricity grid and, in turn, the environment.