Most treatises on weeds solely concentrate on the eradication of, or the opposite, useful ways to make medicines, eat or feed weeds to livestock. All are these facts are good to know, but weeds can teach us more. Why do weeds grow where they do? Usually a shrug of the shoulders, and a "weeds happen" look accompany that question.
An examination of weeds growing on our farmsteads, and in our yards will tell us what is going on below, in the soil. As gardeners and farmers we need to know about the terra firma beneath our feet and hoe.
If you are new to your land, or are just thinking of starting a garden from scratch, weed identification can be very helpful. Weeds like certain soil conditions, and can survive the worst environment. I took a walk today in some of our high impact areas and snapped some pictures of places and the weeds that grow there. If you see these weeds, don't locate your garden there without the expectation of a lot of work. Problem weeds can persist for decades in high impact areas. I will stick with common names, and common weeds, and even though some of my impact areas are caused by livestock, people can tread hard on the land too. Native Americans called Broadleaf Plantain, White Man's Footstep.
Location: Barnyard, wet soil, high animal impact during wet weather. Not much grows here during the summer except Broadleaf plantain, dock and sorrel. I doubt this spot would ever make a good garden spot unless you built raised beds and brought in soil and amendments.
Location: Barnyard driveway, some grass, and clover but mostly pineapple weed. 
Barnyard, high animal impact during wet weather. This area receives full sun and is covered with dog fennel, and some pineapple weed. Sometimes both of these weeds are known as Chamomile.
Barnyard, high animal impact during wet weather. This area is even wetter as the buttercup or ranunculus shows. Ranunculus roots are very toxic to pigs. 
Garden, with the dreaded quack grass. Quack likes a hard pan, if you can correct that, you can make the quack leave.
Quack grass propagates by rhizome. If you want more quack in your garden till it, and chop it up into little pieces. The more you till, the more you will have. It will thank you.To get rid of quack, plant annual cereal rye and summer fallow. The rye breaks up the hardpan and has allelopathic properties that have a lasting effect on the quack grass.
Area near the barn, with high animal impact. Canadian thistle loves acidic and nitrogen rich soil. These spread by underground roots, tilling only gives you more thistles. Cutting just at bloom time will weaken the plant and eventually they will die out.
Pasture near the treeline, this area shows good grass growth, but the bracken fern is still persisting. Timed grazing, or mowing and generous compost applications would help this area.
Our most persistent weed - Himalayan blackberry. This species is very invasive, this shoot in the middle shows this springs growth, already 45" tall. The berries are good, but these plants get so dense and thick, and are so strong they are hard to eradicate.Most of these weeds don't bother us too much, in our sacrifice areas near the barns there is no need to do anything for soil improvement, since we are not changing the use of these areas. The weeds are the earths way of protecting the soil. Irritating as they may be, they are just doing their job. It is our job to observe and learn from them and make changes if necessary.
What weeds, if any, are the bane of your life?
