If the problem is scale and hardness, use a real ion-exchange softener. If the problem is chlorine, sediment, VOCs, iron or another contaminant, choose filtration designed for that contaminant. Some homes need both.
What a true softener does
A conventional salt-based softener uses cation-exchange resin to replace calcium and magnesium hardness ions with sodium or potassium ions.
Its main job is to reduce hardness scale and produce genuinely soft water.
What a whole-house filter does
Whole-house filters can use carbon, catalytic carbon, oxidation media, sediment filtration or other technologies. The target may be chlorine, chloramine, iron, sulfur, sediment, VOCs or another contaminant.
There is no universal “whole-house filter” media that solves every water problem.
When you need both
A city-water home with high hardness and chlorine may use carbon filtration followed by a softener. A well-water home with iron and hardness may need oxidation/iron removal followed by softening.
System order matters because upstream treatment can protect downstream media.
Do not confuse salt-free conditioning with softening
Salt-free scale conditioners may alter scale behavior but generally do not remove calcium and magnesium the way ion exchange does.
If your goal is zero hardness, verify that the system actually removes hardness ions.