What does the low-power mode enabled do?
This is meant to be to show the time&date&weather when the device is pulled out the pocket without waking up the device with the power button.
You can try it following these steps:
- lock the screen with the power button
- cover the proximity sensor at the top for a few seconds
- uncover the sensor
- The clock should appear in blue for a short time.
(I am not sure how reliably this works on newer Sailfish versions. It worked well on older releases but Jolla might change this because on some Sony models there is a problem with the proximity sensor when the device is in a deep-sleep and they couldn't fix that. Then they decided to switch this off when a device goes to deep-sleep. What I am not sure is whether they did this for all devices or just for Sony devices.)
No, these don't need to reapplied after reboots.