It may seem futile to pull certain weeds this late in the season. Those in unrefined parts of the garden that get little or no irrigation might be so dry that they only deteriorate and scatter their abundant seeds when pulled. The soil may be so dry that roots are difficult to extract, especially since the drying foliage now separates from the roots so easily. The only hope is that removal of dying weeds might eliminate at least some of the seeds for the next generation of weeds.
Foxtail and burrclover are not only annoying, but are also dangerous to dogs and cats as their seeds mature and dry. After all, the seeds rely on animals for dispersion, so intentionally stick to fur. The problem is that seeds can get stuck in more than fur, and sometimes get into ears, eyes, nostrils and elsewhere. Seeds from a few other weeds can do the same.
Cheeseweed is not a dangerous weed, and is relatively easy to eradicate. The roots even stay attached to the stems when they get pulled. The problem with leaving them to mature is that they become infested with rust (a fungal disease) that spreads to other desirable plants. Saint John’s wort, snapdragons and roses are particularly susceptible to rust.
Feral Jupiter’s beard and montbretia that grow where they were not intentionally planted are often allowed to bloom before getting pulled. However, after bloom, stems separate so easily from roots that most of the roots remain to regenerate as soon as they are able. If left long enough after bloom, both Jupiter’s beard and montbretia sow seeds to infest even more.
Fortnight lily (or African iris) are not often a weed, but can get that way if their seed capsules are not removed before they mature and pop open. Besides, development of these capsules diverts resources from continued bloom. It is best to remove the capsules before they get floppy, and to remove as much of the finished flower stem as possible without removing stems that have not yet bloomed.
Both dusty miller and coleus are grown for their distinctive foliage but not their bloom. Flowering stems stretch and exhibit inferior foliar color and texture, so can actually get snipped before they bloom.
Weeds are weeds because they grow where they are not wanted. They might be desirable plants in the wild within their native ranges, or beyond their native ranges where they are useful, but for one reason or another, are undesirable in other situations. In fact, many of the most invasive exotic (non-native) weeds were imported because they were useful for something, and then escaped.
The last green roof that I wrote about was planned, although not in a typical manner. 
Plants are quite ingenious with their technology of exploitation of animals and people. Many get insects, birds, bats, spiders and anyone who is animated within their environment to disperse the plants’ pollen for them. Plants who prefer to not rely on wind, water or gravity to disperse their seed exploit a different range of animals to do so. They know how to compensate for their immobility.
Tony Tomeo 