Thanks for the tipYou don't really need them for anything. The only thing they do is fill the gap around the hub and make it a bit easier to install the wheel on the car.
A couple things to watch out for here- Aluminum rings are prone to galvanic corrosion and can get stuck on the hub or sometimes inside the center bore of the rim. Plastic rings will melt if the brakes get too hot.
Also, if you have not already done so, get a set of 19mm spline drive lugs. Many aftermarket rims have small lug wells and a standard socket or lug wrench will either gall the inside of the well or just not fit at all. Spline drives make things a lot easier.