When you change the Conductivity of your CZE method, the following changes can be expected.

Joule Heating: Reducing or lowering the conductivity will reduce the amount of Joule Heating in your capillary.
Current: A lower conductivity results in a lower Current.
Resolution: When conductivity is reduced sample loading can be adversely effected.
Migration Time: A greater difference in Conductivity between the sample buffer (sample zone) and your run buffer will speed migration time. This is called Stacking.