If you have hard water (calcium), a softener system makes sense from a convenience perspective of less maintenance since calcium is more soluble in hot water. Every other water issue should be looked at individually based on tests and or desired correction. For example, if your desire is to remove chlorine just about any active carbon filter will do the trick. Brita filter, undersink filter, refrigerator filter, even whole house. But if you need to remove arsenic (don't laugh, bug issue in parts of the US) then you may need softener/ion exchange + RO. It is very regional and based upon desires and the water in the geography.
If installing whole house anything, remember you may have certain parts where the result is not desired. For instance, if you install a softener and you have a plaster pool you should bypass the softener from the pool fill line or be prepared to buy and dose the fill water with calcium chloride or risk the pool water leaching calcium from the plaster walls. Irrigation, homebrewing, etc. may also have particular needs the filters or softeners can strip out.