We use bacteriophages for their inherent property, as bacterial killers. We use bacteriophages to fight common infections, biofilm infections, and specifically those that are antibiotic resistant.
In their simplest form, bacteriophages are bionanoparticles than can propagate themselves and self assemble. These properties make bacteriophages more powerful than synthetic nanoparticles.
Bacteriophages are very effective at finding and specifically targeting their host bacteria in nature. We use this property to design better diagnostic tools.