It might not be as time-consuming and resource-intensive as you probably think, it is rather valuable information, making it easier to improve and follow-up emissions in the future.
Emission calculations give you
an analysis of your carbon emissions across the entire value chain
an overview of the total company emissions, or specific routes
an overview of the company's environmental impact
a tool to make it easier to set environmental targets
the results point the way for good emission management
documentation of parts of the company's total social responsibility