Again, the end of a thread has stimulated a new point to focus on.
An important step in the composition of big/long forms is the planning. It's due to the more large and complex amount of things to organize, that makes very difficoult to proceed improvisating or casually following the instinct.
But the structure of even very little/short pieces, (it's possible create them as pure improvisation or totally free writing) can be planned in the same way, if the aim is very precise, or the material is selected accurately, or a special language or style must be used etc. etc.
A wonderful sample are the ultra-short string quartet of A.Webern, where in few bars and few seconds the whole power of a 12 tunes serial structure, and the maximum variety of sound expressions and dynamics, are condensed in a micro-universe. Every single note is planned and has a coherent relation with the total of the composition.
It's probably the extreme limit for concert pieces, but simpler samples exist in the whole history of music, frequently for didactic purpose
(e.g. from the piano "sonatina" of M.Clementi, a sonata form condensed in few minutes of music for beginner pianists, to Bartock's Microcosmos, with the same aim).
All those pieces were impossible without the same accurate planning of a large Symphony or Concerto.
But the natural objection is: how much the planning is limiting the artistic level, or reducing surprise, or standardizing the writing?
The answer is in another question: how much freedom make writing unbalanced and cahotic? How far can you go without a plan? How long, slow and heavy is the work, if a plan doesn't help you avoiding repetitions, developing ideas and keeping all coherent and balanced?
The last clever point is: you are human, your brain will unconsciously plan even if you try improvisating or you write step by step what the inspirations suggest.
Only a really random process should be unchained by the power of planning of the brain, but probably for the same reason, rarely satisfying from an artistic point of view!
Let's start a useful presentation of your planning method and suggestions!