Hub centric rings center the wheel bore on the vehicles hub. In most cases, the wheel bore with be larger than the vehicle hub. One of the reasons they do this, is so the wheels will be more "universal" and fit more vehicle applications. If your wheel bore is 73.1 and the Slingshot hub is 66.1, you would want a 73.1 to 66.1 hub centric rings. Preferably the more expensive metal ones.
https://www.amazon.com/Hubcent…T=_SY300_QL70_&dpSrc=srch
With them installed, know have eliminated the play between the wheel bore and hub. Less play means less stress on wheel studs and overall better balance of the wheels.
Most people buy these after the fact when they are chasing issues on thinking a tire/wheel isn't balance correctly.
You should buy and install them. It is a cheap investment to make sure what you install is correct and as good, or better, than the factory take offs.