Gross profit is the pool that has to cover research-and-development, sg-and-a, interest, tax and whatever is meant to be left over for owners. It is the cleanest single measure of how much value the product itself creates.
Because it is measured before overhead, gross profit dollars are often a better scaling measure than revenue for marketplaces and resellers, where the top line depends on gross-vs-net-revenue conventions.
Example: Northwind Tools has revenue of $840M and COGS of $470M, giving gross profit of $370M, or 44% of revenue. That $370M has to absorb $250M of operating expenses before a single dollar of operating profit appears.
Related: revenue, cost-of-goods-sold, contribution-margin