Your question is a good one, thanks for asking it.

I too have cleansed with white sage, sweetgrass, and copal and they are effective. The actions of burning sage and copal is the way the cleanse is applied. Burn sage and copal for example bring in high vibrational energy to a space and my assumption has been that disorganized or negative energy is released as a result.

If you're familiar of the principles of homeopathic and allopathic medicine then the following analogy may make sense.

Sage, sweetgrass and copal act as homeopathic introducing light as a way of cleansing. Ghosts may run and hide during a smudging depending on the level of their attachment. Strong attachment - then more running and hiding.

The burning salt technique is a targeted approach. It targets the negative elements of attachment (much like an antibiotic works). The negative energy is separated from the ghost or even from ourselves, and/ or the disorganized energies in our spaces an grounds them into the salt. Putting the salt in the ground using sacred rituals as part of our intent completes the process. And that is the difference.

Mainly it feels different after completing it. I've done it in my own place and for a business and other's homes too. It feels so good in the other places where I've done it that I've wanted to hang-out (and/or move in there). :)