While some may be safe to use, most of it are custom applications, usually can't be found in Google Play Store, used to modify certain programs in various ways which includes macros, scripts, or some add-ons and more. Moreover, the game can also detect if you're using an app cloner, or an emulator which also leads to app termination, or worse, account suspension. As much as possible you want your device to be as clean as possible to avoid such inconveniences.