Custom kernels have been long used to increase performance on Android devices. Think of the kernel as the base that the OS and UI sit on top of. The kernel pretty much tells Android what it can and can not do. By adding a custom recovery you can overclock your cpu and increase its performance. You can also mod your screens colors, and there are all kinds of extra things you can do with a custom recovery.
Another use for a custom recovery is the ability to lower your CPU speeds to increase battery life. There are also governors which can be set to help with battery life. Many of us have portions of our day that we are not heavily using our phones. These are the times where you could turn on a power limiting governor to save your battery for later in the day.
Developer "Ktoonsez" has released a custom kernel for TW 5.0 on the T-Mobile variant of the Galaxy S6. You can use KTweaker to change your CPU settings once you have flashed the custom kernel. If this causes any issues with S-Health simply force stop the app and clear its cache. Grab the kernel below.
via XDA