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Ring flashes are best suited for super-macro, or subjects where the working distance makes it difficult to pull your external strobes in close enough for even lighting. The ring flash improves these images by producing more even lighting and softens highlights otherwise produced by awkwardly placed strobes.
There’s also a convenience factor for using the ring flash. On dives or trips when macro is your primary incentive, you can just leave the ring flash on to limit time wasted moving your strobe’s arms again and again, as is the case with traditional lighting. This leaves more time to focus on composition and creativity, and less time worrying about on strobe position.
While it is an extra financial investment and takes some time to learn, using a ring flash can actually be simpler to assemble and use than traditional strobes. With reflective-style or fiber-optic ring flashes, it’s also easy to remove the ring flash if you want to experiment with back- or side-lighting.

For those who love to take macro images and don’t want the hassle of constantly adjusting strobe position, a ring flash can be an indispensable tool. With the light provided in a circular pattern as close to the subject as possible, it allows the photographer to change between portrait and landscape composition without the need to constantly adjust strobe positioning.
Being lightweight and compact also allows the light to reach into cracks and holes that would otherwise be impossible with traditional strobes. This is especially important when working with shy subjects.

The settings for using a ring flash are, in many ways, similar to using a traditional strobe setup for macro. The only additional consideration is when using a fiber-optic ring flash. Some of the strobe output will be lost as it travels from the strobe to the device on the port through the fiber-optic cables. Thus, make sure to compensate either through a more open aperture or higher strobe output.