It's not that SWGs are "different", it's that when running properly they have two advantages over other chlorination systems:
1) They are constantly gen'ing chlorine at low levels. You don't actually need a lot of chlorine to keep your pool sanitary, but it has to be able to respond to demands on it--like people and suntan oils, etc. A residual level gives you a safe lee-way or metabolizing stuff will drop you below that sanitary level, leaving your water vulnerable to contamination. But an SWG takes over for that
2) They super-chlorinate the water that passes through them, killing everything in it.

Remember: SWGs ARE chlorine systems and follow chlorination rules. But rules of thumb may not be as applicable.