Doh!
OK Mr man-in-the -street:
See that runway, in fact any runway, anywhere any time? Well with QFE set - when the altimeter reads zero you will be landing on it.
See that hill just over there? The nice man / lady in ATC or the little book of Approach Plates I carry that tells me how to get to the runway also tells me a height not to fly below so that I can be sure to miss that hill.
When we fly away from the airfield but stay quite near the ground I will set the QNH on the altimeter so that I know how high I am in relation to the sea level cos that is the datum height my maps use to show me how high the hills are. But just like the QFE thingy - we'll need to change it every now and then cos the pressure over the country changes you know.
And if we go high, no matter where we are we set SPS so that we can all miss one another.
Easy isn't it? - no matter where I go or how busy I am I know that the runway = zero on the altimeter with the QFE set and there are only the other two thingys to remember when you arn't quite as busy.
Now would you like to be patronised about any thing else?
