What happens if flux is not used in welding?

As a financial professional with an interest in industrial processes, I'm curious about the role of flux in welding. Could you elaborate on the potential consequences if flux is not used in welding? Specifically, I'm interested in understanding how it affects the weld quality, strength, and durability. I imagine the lack of flux could lead to impurities in the weld, but I'd like to hear a more detailed explanation of the potential issues and how they might manifest in practical applications. Thank you for your insights.