Dryer balls help your clothes dry faster by absorbing moisture. It also helps your clothes open up as the dryer tosses them so air passes through them better, which helps dry items faster and more thoroughly. It also reduces wrinkles as clothes “open up”.
I use them especially when I wash large bedsheets as I used to end up with sheets that were still wet at certain portions that were being clumped together. It also acts as a natural fabric softener by reducing static!
I gave it a “green” tag because drying the clothes faster means less electricity is used!
P/S: I know some people use tennis balls instead. However, the glue and rubber will give off VOCs under the heat of the dryer which may not be good for us in the long run as we wear our clothes close to our bodies for long hours and may breathe in or absorb the VOCs that latch on to the fibres of our clothings.