I've been having an interesting conversion during my exploration of sonnet writing. Being a child of free verse, I have always thought the sparer the better, write and then take a scalpel to it, keep only what's fore-grounded. However, I have begun to consider the idea of background notes in a sonnet, words which would be cut away as superfluous in free verse, but which offer an on-going tempo. Sometimes the rhythm in a poem needs to be ragged and destabilising, at other times it can be like the underlying beat of feet or drum, giving scaffolding to the melody.
According to Ruth Padel (on Radio 4's "Poetry Workshop", Sunday 25th November 2012) poet Louis MacNeice believed in the need for the containment provided by form poetry and metre. She quoted from his poem "Snow":
World is crazier and more of it than we think,
Incorrigibly plural. I peel and portion
A tangerine and spit the pips and feel
The drunkenness of things being various.
Perhaps the dependable iamb of the sonnet offers a fluted vase for the craziness, a handrail for the appalling drunkenness of the world we poets are attempting in some small way to engage with.