What happens if you weld without flux?

Could you please elaborate on the consequences of welding without flux? I'm curious to understand the technicalities involved. Would the absence of flux affect the quality of the weld significantly? Could it potentially weaken the structural integrity of the welded joint? And, what specific issues might arise in terms of porosity, incompleteness, or other weld defects? I'm interested in gaining a deeper understanding of the role flux plays in welding and how its absence might impact the overall process.