For me, guided meditation is useful when it is difficult to concentrate attention, when I am distracted. When I feel more calm, normal meditation is better.
I am not sure. I think that guided meditation is easier. Especially if you haven’t been meditating very long. I think it can help you learn and get better at it. I think, though, that it is important to practice meditating on your own, as well, without a guide. I think both are equally important and beneficial.