Weeds are troublesome in many ways. Primarily, they reduce crop yield by competing for water, light, soil nutrients, and space. Other problems associated with weeds in agriculture include:
a) reduced crop quality by contaminating the commodity;
b) interference with harvest;
c) serve as hosts for crop diseases or provide shelter for insects to
d) limit the choice of crop rotation sequences and cultural
e) production of chemical substances which are toxic to crop plants
(allelopathy), animals, or humans.
It's funny because I also read a text that mentioned the benefit of weeds. Getting rid of weeds takes a lot of effort and work. You have to get out there in the sun and literally rip them from the ground. What a backache! Limiting the amount of weeds also takes a lot of effort and work. It requires you to be selective and making sure that you only sow clean seeds. In some crops, weeds can often help to shield those crops from the blowing wind. However, in the end, if you allow the weeds to stay long enough, they may protect you from the winds in the short-term, but they will eventually do what weeds do. Decrease your crop and lessen, if not destroy, your harvest.