According to Apple’s developer documentation ‘Always’ allows the app to: (1) start tracking your location whenever it is woken up in the background (e.g. via Background App Refresh), (2) ask the system to wake it up in the background when the device detects location or boundary changes.
It depends on what you are doing with this application, but generally location services are very energy-intensive. Google can also use these permissions to stay awake in the background virtually forever and record every moment (and they actually do this).