Battery Health Management will only be available to MacBooks with Thunderbolt 3 ports (2016 and later MacBook Pros and 2018 and later MacBook Airs) and is designed to slow the aging of the internal battery by looking at how you charge your device and acting accordingly.
So, if you keep your MacBook plugged into the charger a lot, the software will not fully charge the battery to 100% in order to preserve its quality. Frequently fully charged batteries that stay at capacity will wear down faster.
The software should help by identifying how you use your charger and make changes to the flow of electricity to the battery. If it sees you frequently run down the battery to near dead, then plug it in to 100% before unplugging immediately, it will charge it the whole way up rather than stopping short.
You will reportedly be able to switch the setting off, but it is on by default. It sounds to us like something you should definitely keep switched on and will help you get the most out of your expensive MacBook before the battery no longer holds a charge.