Are flies pests or beneficial? Depends on the fly. It also may depend on who you ask! Some are pollinators; some are predators. Here are flies from last year’s garden.
Tiger bee fly:
Common green bottle fly:
Unidentified dead flies, likely killed by a fungus. Other people have posted dead white flies like this on bugguide.net; University of Minnesota Extension has a potential cause.
The end of a robber fly:
Small and large hover flies: