Weeds:
- Crowd out plants
- Propagate like crazy through runners and seeds. If there is open ground weeds will be found!
- Are just plain annoying.
- Block the sunlight from reaching the vegetables and ornamentals.
- Suck the moisture away from the vegetables and ornamental plants.
- Sap the nutrients from the soil making them unavailable for the "good guys".
- Are always where you don't want them. But then again, if you wanted them they wouldn't be weeds.
- Can take over large areas in a very short time. They grow fast and few barriers can really stop them.
- Have the annoying habit of working their way into places you can't reach.
And if you want my personal opinion, piece the italicized words together to make a sentence!