So there is a logical reason why I am totally overwhelmed and feel like a complete idiot when trying to understand basic units in electrical engineering.
Units in electromagnetism are a fucking quagmire built on inadequate understandings and deep seated biases. I also now understand why Eric has such distaste for physicists and their attachment to electrons and mass.
After reading the following article I can appreciate so much more what it is Eric is trying to accomplish.
The rest of that guys site is a goldmine for trying to navigate units and equations in electrical engineering. Highly recommended.
Hat tip to Garrett for the find.
So, the answer to our original question "Why use different unit systems?" is not simple reluctance to change. It is, as Ken Alder says, about what you hold to be important. Pragmatists favour the SI's utilitarian approach to calculation, want all the factors of c kept out of sight, accept the embarrassing units for km and will never replace a 3 abampere fuse. OTOH, philosophically minded physicists want only the three base quantities of the Gaussian system to better reflect the underlying science. They dream of a visit to Woolworths where they enquire of the sales assistant
"Excuse me, have you any 600,000,000 ergs per second light bulbs?"
"Why, certainly, sir. We sell all our electrical goods by Gaussian units because in advanced texts on electrodynamics we find that the tensor calculus equations which unify the electric and magnetic fields are just so much clearer!"
"Great, I'll take 59,958,491,600 / c of them, please."
"While you're here, may I interest you in our five millistatvolt AA cells?"
Stuck in between these groups are the engineers; we must cope both with text books written by the latter and problems set by the former. Whatever your own view may be, don't expect a truce soon :-(