Quick take
It is usually worth it when measured hardness is high enough to cause persistent scale, soap inefficiency and appliance buildup. It is less compelling when hardness is mild or the household only cares about drinking-water taste.
Benefits that justify the cost
True ion-exchange softening reduces calcium and magnesium, which can reduce scale on fixtures and heating surfaces and improve soap performance.
What a softener does not do
A softener is not a substitute for carbon filtration, PFAS treatment, nitrate removal or microbiological treatment.
Operating costs
Salt, regeneration water and occasional maintenance are ongoing costs. Smart metered softeners reduce unnecessary regeneration compared with simple timer-based systems.