That is the question. Fruits and vegetables like pole beans, peas, cucumbers, melons, tomatoes, squash, and sweet potato prefer to grow vertically, and with good reason! There are many benefits to using a trellis or support when growing fruits and vegetables.
Increased sun exposure is a natural benefit from trellising. By increasing sun exposure to your plant, you are ensuring a healthier crop, more growth more quickly, and higher fruit yield. Trellising can drastically improve airflow as well. Crops like cucumber and squash are notorious for contracting powdery mildew at the peak of summers heat an humidity. One of the main reasons these crops are more likely to develop this disease is because of airflow and circulation. Cucumber and squash plants have little tendrils that grow along each plants stem. These tendrils are picky and prefer to grab onto organic material like twine or wood while reaching up in hopes of new heights. Using a trellis while growing these crops encourages this natural behavior, and give the plant something to grow upwards away from the ground while naturally increasing air circulation.
Growing crops near or on the ground encourage disease. Yet another reason to consider vertical growing practices. Each time we water or use a liquid when fertilizing crops there is liquid that splashes from the soil onto the plant. This liquid containing potentially harmful soil bacteria could easily get onto fruit or an unproperly pruned branch and spread disease quickly. Which brings me to my next point, pruning... and harvesting. We spend a lot of time tending to these crops, and much of that time is spent pruning and harvesting. Using a trellis to support each plant encourages up and outward growth which makes pruning AND harvesting a lot easier for the farmers.
Although trellising is not a must, it is strongly encouraged. There are tons of benefits and beauty to vertical growing.