Controlling or eliminating weeds is a necessity, not only for esthetic reasons but also for ensuring the good health of your plants.
These plants that we call "weeds"
It is true that there are not really weeds, just plants that arrive and are unwanted. It might be better to call them undesirables, because they can often be good for other reasons such as being edible or used as fauna. This does not however stop a garden that is overrun by them looking neglected. A bunch of nettles in the middle of a flowerbed ruins everything. From this point of view, weeding is esthetic.
However, the main reason for weeding is to reduce the competition that these unwanted plants provide to the cultivated plants! It is a lot greater than we often believe. Nearly always, the plants that we grow are not found growing locally. We often use our gardens for plants that come from very different areas, be it from Europe or elsewhere. Compared to the locally found wild plants, these cultivated plants are less well suited to the conditions found in the garden. Weeds often establish themselves by means of seeds taking root wherever they land. They are perfectly adapted to the local conditions (if they were not then they would not appear) When a weed installs itself next to a cultivated plant, in nearly every case it is better suited to fully exploit the food in the soil.
LWeeds therefore create a lot of competition for cultivated plants. The roots of the weed “steal” the nutrients from the soil at the expense of the cultivated plant. As the weed is better fed it grows better... and steals the light from the cultivated plant, which ends up being penalized twice. If the gardener does not intervene then the law of nature will prevail. It is therefore important to weed at least until the cultivated plant is strong enough, that it is not bothered by the competition from the weeds.
The other problem with weeds is the chance that they might transmit certain diseases to the cultivated plants. If plants are under cover (greenhouse, polytunnel or veranda…), it is a classic case: where do all the greenfly that swarm over the seedlings in the spring come from? Often it is from the weeds hidden in a pot, that provided shelter for the greenfly over the winter…so they can attack your tender plants at the first chance. In the garden, it is the same thing. A vegetable plot surrounded with weeds (even if the area used for growing is clear) is more susceptible to certain diseases.
Weeding is therefore not a question of things being good or bad. It is a means of ensuring the best development of your cultivated plants. You do not need to be obsessive: good weeding does not mean removing everything, but only those things that need to be got rid of.