A theme can be done abstractly and subtly using color, lighting, sounds, and flavors versus going overboard on needless decorative items from the dollar store to fit the Hawaii theme you are aiming for. And if things aren´t done right, the downside is that it can wind up being kind of cheesy or over the top expensive if you choose to include that erupting volcano prop as well.  If you are currently on the fence on whether or not to include a theme or just do a traditional type wedding here some pros and cons about theme wedding ideas.