Where are signal jammers generally used? Is there a specific place?

I would like to know where they are used and what is the purpose of using them, can you tell me?

Topsignaljammer  2022.

Places where signal blocker are generally used:
1. Protection of communication signals of border operators
2. Troop combat needs
3. Detention centers, labor camps, large and medium-sized prisons
4. Large gathering places
5. Safety precautions for leaders to visit
6. College entrance examination, adult college entrance examination, self-study examination and various colleges and universities
7. Party and government organs, various large, medium and small conference rooms, concert halls, theaters
8. Gas stations, oil depots, oil fields, gas stations and other flammable and explosive places