The direct cash loss from weeds is in lowered crop yields. Weeds rob the crop of moisture, nutrients and sometimes light. And they usually mean more trouble and indirect losses- in combining, later weed infestations, etc.
Staniforth, David W. and Weber, Charles R.
"A New Slant on Weedy Beans,"
Iowa Farm Science: Vol. 11
, Article 9.
Available at: https://lib.dr.iastate.edu/farmscience/vol11/iss9/9