Notation should be considered a set of instructions for performers. And nothing else.
Notation is not art, nor is it a program note. Perhaps most importantly, it is not music.
Augenmusik is useless at best and destructive at worst. Baude Cordier, George Crumb and others were wrong to use it. This fact does not diminish their value as composers – only as copyists.
The quality of a composer’s musical idea is distinct from his/her ability to notate that idea. Composers who lack the desire or technical ability to notate clearly should hire copyists.
If an extramusical-idea-as-notation is necessary for a composer to move forward with the composition, then this version of the notation should be thought of as a draft. Upon completion, the work should be renotated to facilitate easier performance.
Performers should not be expected to renotate music to facilitate easier performance.
There may be extramusical reasons to provide scores to performers which cannot be played. But there are no musical reasons to do so. Performers who receive such a score should expect/request a corrected version.
If there is a simpler way to notate a given idea, then that is the correct way. There are no exceptions.
Certain instruments – in particular, most percussion instruments – do not sustain. Notation cannot make them do so. This information can be used to, for example, determine appropriate notational durations, ties, etc.
There is widespread belief that obfuscated, florid or unnecessarily complex notation may impress judges in composition competitions. Composers who enter competitions and who work under this assumption should then create two sets of scores: one for competition, another for performance.