At the writers' group the other week, one poet suggested to another that they could chop a problematic line from a poem without too much angst, because the line might still come in handy for a poem in the future.
I've heard quite a few writers recommend this tactic. I've tried it myself and – living as I do amongst several kilos of thwarted drafts – I can see how attractive it is. You can get ridiculously emotionally attached to a metaphor/word picture, considering it won't cuddle up to you in the morning.
And it's hard for folk to clip something so dear to them, that perhaps is dragging the rhythm down, or is just too brand-spanking clever to slip into the tone of this/that poem. So it's nice to think your brilliant image might have its fifteen minutes' fame in the future.
The other extreme is the scorched earth policy where folk rigorously chop out particular types of word – all the adjectives have to go, any phrase or image that seems "lazy"... Often folk give the haiku as an example of the ideal – a couple molecules of distilled image and meaning.
But not all poems are haiku. Nor are images and phrases bits of Lego to click into any poem.
So this leaves the poet in an uncomfortable place where a poem "working" is a rare event to which thought and experience and rhythm and personal idiom and image are bespoke.
And in this arid place, sometimes a line starts in your head and your experience crowds up to meet it. At which times a line you saved specially from a previous poem is usually far inferior to the wealth of perfect accidents you are about to be able to select among.