Up until my third year EM course we have used SI and MKS units in EM. In fact every textbook i have used for EM (griffiths,wangsness) also use those units. My current prof wants up to learn CGS units. While they do appear much 'cleaner' (no epsilon0, mu0 for certain equations) what is their use in the real world? What units would a physicist in his or her day to day life of physics use?? At least in north america... is the cleanliness of expressions the only reason why these units are used??