I've just been reading Samwise's blog about the double use of their broad beans as a climbing support for peas...brilliant!
It got me to thinking about things we do in the garden that have additional benefits.
We have espaliered apples along the fence on our driveway. I plant annuals underneath them to add some interest and a bit of prettiness. SH has been religiously feeding our fruit trees which has had the extra benefit of feeding the petunias I have planted below - first additional benefit.
Second additional benefit - the purple petunia flowers attract heaps of bees which then go on to visit the blossom above and help set the fruit.
The third benefit (which I have just thought of) is that we get to enjoy the beauty of both. Triple bonus!!