Experienced gardeners use raised beds to sidestep a long list of gardening challenges.
The primary purpose of using raised beds is to be able to grow in a custom soil mix because your current soil is poor. The raised bed soil is lighter, fluffier, holds more water and has more nutrients.
Bad soil is out because you fill a raised bed with a customised soil-and-compost blend. Greater exposure to the sun warms the bed, which allows more plant diversity and extends the growing season. Plants can be spaced closely together, so yields go up, water-use efficiency is maximised, and weeds are crowded out.
Finally, raising the soil level by even 20 cm reduces the back-bending effort needed for jobs such as planting, weeding and harvesting.