In Brief: For some reason the creators of the Live Action Sailor Moon decided to use a different tiara attack instead of the anime and manga related Moon Tiara Magic one. Most likely inspired by Sailor V's Cresent Boomerang attack (featured a lot in the Sailor V manga and a variation is used by Sailor V in the Live Action Sailor Moon) Sailor Moon's tiara now transforms into a golden boomerang which can be thrown at an enemy to shock them but without enough power to actually destroy the bad guy on it's own. It's because of this that the attack isn't use that much.
Starting a trend in Sailor Moon attacks, Moon Tiara Boomerang was the first of many attacks in the Live Action Sailor Moon show that did not feature a set attack animation/clip like all the anime attacks. Instead, every time the attack was used, it was performed in real time (unlike say, Mercury Aqua Mist ).

Cultural: Being an Australian I always thought it was cool whenever a tv show used a boomerang (take Batman for example), however being Australian also makes me a bit more educated about the realities of throwing a boomerang, something Sailor Moon obviously doesn't know much about. For example, the throwing style shown on the pictures on this page show Sailor Moon throwing the Moon Tiara Boomerang in a frisbie style throw, though in reality boomerangs are actually thrown with a kind of half flick, half overarm throw to effectively make the boomerangs return. Throwing a boomerang like a frisbie would simply throw it straight ahead and possibly off to the side and cause it to land a significant distance from the thrower.
Whenever the Moon Tiara Boomerang returns to Sailor Moon, it's most likely due to magic rather than her throwing ability.

The Attack: Sailor Moon begins the attack by causing the red gem on her tiara to glow a bright red. The glow increases in power and quickly changes to an incredible gold shine. While covered in the golden glow, the tiara morphs into the boomerang form and is grabbed by Sailor Moon who has had her right hand ready to recieve the transformed headpiece.
She quickly flings the boomerang backwards over her shoulder then forward and down as she kneels into a crouching position. Sailor Moon pauses for a bit as another bright golden glow blasts from the boomerang, obviously a sign that it's powered up and ready.
Sailor Moon quickly throws the boomerang at her opponent.