With Eco mode, you will be able to lower the TD one tier from stock. For example, the Ryzen 9 3950X can be reduced from 105W to 65W, while the Ryzen 7 3700X can be cut from 65W to 45W.
AMD says that by cutting the TDP of the 3950X to 65W, you get up to 44 percent lower power consumption while retaining up to 77 percent of full performance. AMD's internal testing shows this can make the chip run 7°C cooler. The feature cooled be useful for small form factor or low-noise PCs.