They do have the advantage of warming up more quickly than flat soil surfaces in the cooler seasons. Overhead sprinklers that broadcast water will also water the rows in-between and encourage weed growth. It is better to use drip irrigation or a soaker hose in each bed. Small gardens can be easily hand-watered using a hose wand that has a sprinkler head to keep droplets small. The great advantage to raised beds is that only the soil where plants will grow needs to be fertilized.
None is wasted on pathways.
Take a soil test first. Fall is the best time. If soil pH needs adjusting or slow-acting materials such as phosphorus or potassium need to be added, they can be worked into the soil before the rush of spring planting. Plants in raised beds are more crowded and nutrients can be depleted in a shorter time than in conventional gardens. Be sure to sidedress heavy feeders such as onions, tomatoes, and cole crops before they flower or begin bearing.