HDMI 2.1a has received an amendment that adds a new feature to the specification called HDMI Cable Power, enabling active HDMI 2.1 Cables to be powered directly from the HDMI Connector. This allows for active HDMI 2.1 cables that no longer require a separate power cable, a welcome improvement for enthusiasts who have required lengthier runs due to longer distances between their display and source devices but would prefer to have fewer cables to worry about. (An HDMI Source device that supports the HDMI Cable Power feature is required.) Active HDMI cables are recommended and usually mandatory for longer runs in order to maintain the signal and avoid visual impurities.
In the case of the Ultra High Speed HDMI Cable, performance requirements are so high, it is likely that the only way to meet the Ultra High Speed HDMI requirements in cables longer than a few meters is through powered, active HDMI Cables. Therefore, HDMI Cable Power was added to help support the HDMI 2.1a specification’s higher speeds by providing power to those active cables which may need it to function correctly. While active HDMI Cables have previously been used extensively in professional markets, their use will now increase in the home whenever consumers need longer-length Ultra High Speed HDMI Cables.
Source: HDMI LA