As far as opened tabs are concerned, the battery savings are significant. Reportedly, Google was able to save two hours of battery life in a test conducted with 36 background tabs and one blank foreground tab. However, the battery gain reduced to 36 minutes when playing a YouTube Video. Nevertheless, this upcoming feature is a step in the right direction.
The experimental feature is currently available as a flag in early Chrome 86 builds. According to the TheWindowsClub, it will be available for both desktop and Mobile versions of Chrome soon. Although, there is no news whether the feature will be ready by the time the new version of Chrome is ready for mass adoption.
Over the years, companies like Apple and Microsoft have regularly touted battery life advantages over Chrome. Hence, this feature will be extremely useful for Chrome fans.