What happens when a GFCI outlet goes bad?

Could you elaborate on the potential consequences of a malfunctioning GFCI outlet? I'm curious to understand the safety implications as well as any inconvenience it may cause in daily usage. Would the outlet still function as a regular outlet, or would it completely cease to work? Additionally, are there any warning signs or symptoms that indicate a GFCI outlet is on the verge of failure? It would be beneficial to know what to look for to avoid potential electrical hazards.