There are several advantages to raised beds: they warm up and dry out faster in the spring, the soil doesn't get walked on, and they can generally be planted more intensively than in-ground beds, making the use of space more efficient. They are also useful for spaces where the soil is poor (or non-existent) and for gardeners who have physical difficulties gardening in the ground.
Despite what some authors would have you believe, however, there are some disadvantages to raised beds. Beds created without walls tend to erode away and are not as attractive, while beds with walls can be difficult or expensive to build. If the walls are sturdy and don't start falling over in a couple of years, weeds and lawn grass will inevitably squeeze up right beside the walls, where they can be very difficult to eradicate. But the biggest problem in areas with warm summers is that they dry out very quickly in hot weather, and can require constant watering.
Are raised beds better? They definitely are if you're trying to garden on rock, but otherwise it just depends on your situation. In any case, they are easiest to build and dry out more slowly if you don't build them too tall. Unless you can't bend over at all, there is no need to build them any taller than about 6 inches. And it's probably wisest not to have grass paths between your beds, unless you want to be ripping grass out of them forever.