Often I think that bringing a ring flash to a photo shoot is like bringing a knife to a fist fight. There is a point of no return when you decide to do it and you better hope the stars are in alignment for the gambit to work. Due to the setup time and luggage carrying toll of deciding to use a ring flash, it really isn’t practical to be “testing” out whether the lighting idea will work out on most shoots. Unless you are lucky enough to have very patient subjects and a lot of time on location, most event shoots require the photographer to be up and ready to shoot as soon as possible and get subjects having a lot of fun and being silly instead of watching the photog fumble around with light modifiers.
There are definite pros of bringing a ring flash that allows you to shoot very distinct portraits and close-ups: nice even lighting, unique outline shadow around the subject, and for the most part, flattering to most subjects (with super pale skin being the exception). You have to know how to wield it properly though, you can’t just go willy-nily and use ring-flashes in random situations. It’s a very particular look that can get over-played if you are not careful. When it does work though, it’s a super awesome way to get great face pics without too much adjusting on the fly. Just be prepared for the initial shock of your subjects seeing a giant circle of light right in front of their faces haha.