I don’t know why Amir does it, but I do it for two reasons. It’s easier on the back, and it’s harder for snails and insects to invade vs being planted in the ground.
I hold some experience in that field, so I feel that maybe I can help in one way or another, at least sharing my experience. My English is quite limited in this field but I'll try to be as clear as possible.
For the back, replace the handle hoes for larger ones. Accommodate the tool to your need, not the opposite. Buy or rent a motorized plow can help a lot.
With respect to snails, indeed they are one of the biggest enemies of certain vegetables, however, there is something more important to be considered here, in my opinion and based on my experience.
Plants are very complex beings that require a combination of many different conditions to give the best of themselves. To reach that, the best we can do is acknowledge and respect their needs and preferences instead of imposing ours to them. And if one has to express this with one word it would by this: diversity.
The plants we grow in a vegetable garden are like any other plant, with the same needs and preferences. Therefore, when you see a vegetable garden than only has vegetables, or "good" plants, normally means that is not a healthy and rich ecosystem for a plant. The diversity of an ecosystem is the best measure of its health. Therefore, don't be afraid of any plant or animal in your ecosystems. Exactly the opposite: the more diverse, the better for your plants. If there are some insects, some birds will show up, which in turn will leave their valuable excrement. The processes by which the roots of the plants extract water and nutrients from the soil is very complex and usually involves other plants roots and fungi which live in symbiosis with the plant roots, but they need the soil to be rich to flourish. Therefore, if other "undesired" plants grow along with you vegetables, let them be, just control they don't get too large. The most productive natural vegetables gardens I've seen are the most chaotic ones, with lots of undesired plants.
If you try to create a separated and controlled environment, which seems very reasonable in electronics and most of sciences, you are creating a poor ecosystem, which may look healthy for a human eye: clean, ordered, etc. But it has almost nothing in terms of chemical diversity, which is in the end what allows the plants to grow tasty seeds and fruits.
My advice is this: if you have a piece of land that you can devote to vegetable gardening, before planting anything valuable, try to build a rich and diverse ecosystem. Start by adding some external nutrients by means of excrement or chemicals and plowing that piece of land, increasing the amount of oxygen and nitrogen of the soil to facilitate all that decaying process which creates the food for the plants. That is, we limit our action to help that natural processes to occur more quickly by creating an environment ideal for the the decomposition processes of organics. We do that every time that we plow the land, taking the nutrients from the first inches to a more deep stages, where our plants will find them. Once that piece of soil contains some tasty organics for the plants, they will start to grow naturally. This is the first sign of success. If you see that there are too much aphids, you can buy a colony of ladybugs, which helps a lot to increase the ecosystem diversity. Once those first plants eventually die, don't do anything at all. Just let them decay there and after few months plow the land again and start over the process. That depends heavily on you climate though. However, some decomposition must reach the land, so if because of your local climate, the periods where the plants naturally die are very short, just cut them once a few months, to allow for decomposition and others to take their place. Plowing more often in that case will help to ensure that nutrients don't stay only at the surface, as it happens in rainforests.
This process can be combined with productive ones. For instance, you can grow some vegetables half of the year and leave the other half to mother nature. Also, consider that fallow is the most important discovery in the middle ages with respect to agriculture, so, let the land rest if you can afford it.
Following that simple rules, in few years you can have a very rich ecosystem that eventually can reach that magic state of equilibrium, in which you don't have to do anything but make some place for your plants plowing a region, water, collect, and leave it in peace until the next ones. Now you can think, ok, but I want my tomatoes right know. Let me tell you something: you won't get them until you have a good place for them. Yes, you can grow anything with a lot of external chemicals and effort, but it will have a fraction of the taste and properties of its ideal version.
And finally, when you have achieved all of this, then and only then, you can start worrying about snails and other plagues.
All of this is very hard to achieve if the piece of land is physically separated from the rest, as it will be more difficult for earthworms and other important animals to invade you ecosystem and will create an effect of isolation which is exactly the opposite that is required for a healthy ecosystem. These are open systems, never isolated. An isolated ecosystem will always eventually die, become inert. You can try to sustain it artificially by adding a lot of products, but you will be putting there just a fraction of what it needs, which is very complex. Yes, in some industrial monoculture plantations everything is absolutely controlled. However, that requires a lot of knowledge and resources, and usually they are only aimed to achieve size, but not taste or properties. Also, those physical impediments will difficult the vital task of plowing, which requires to be done at a depth of 30 - 40 cm.