Advantages: 1-Operate at ...

Advantages:

1-Operate at higher cycles of concentration.  The biggest savings are getting up to around 50 COC with diminishing returns to a practical max of around 75.

2-Less scaling potential.  Your boiler should be much cleaner come inspection time.

3-Boiler chemistry cost reduced up to 70%.

Disadvantages:

1-Greater operator attention than a water softener.

2-Higher operating costs, especially in electricity.

3-Capital cost.

4-Make sure the metallurgy of your feed piping can handle the more corrosive feed water.

Like everything else, it comes down to payback.  For most applications the payback is favorable over 2-3 years at most.  The cleaner the feed water and lower the pressure boiler, the longer the payback.