As far as I know, the only advantages to using potassium are:
1. That it will eliminate the (very slight) salty taste your water may have.
2. If your discharge line drains into your yard, over time salt accumulation may kill anything growing in that area - but usually that only happens when you're using too much salt for each regen cycle. If it drains into the sewer system, no problem.
Our discharge comes out salty, but it's been draining into the same part of the yard for over 25 years, and the grass there is alive and well. I really think it's a matter of personal preference.