Why do so many ignore the original question instead of helping?
Here is one scenario why LPM is a good thing: At my workplace, the building basically is a perfect Faraday cage. The result: If I had, for instance, left Mail open and not be on LPM, it would regularly try to fetch mail. Thus, the phone tries to connect. (For many other Apps/processes the same applies). Unsuccessfully.
Result: Battery is draining like hell (Battery usage report: 'no mobile coverage').
On LPM, that is not happening / way less, since in this mode, background App refresh is minimal.
Thus, this is a perfect usage scenario for LPM.
OK, I would not shut down to achieve the same, rather would just turn off Mobile data, but maybe that's more cumbersome to the thread starter - his/her business. LPM is easy to get from Control center, so that's why I prefer to toggle it.