The use of a high degree of rhythmic detail in such a score, instead of prescribing a particular effect, has to do with directing the performer away from more habitual modes of performance.
I'm not quite sure that I understand what you mean by this, or indeed the specific kinds of context in which you see it as being applicable; I have always though and hoped that the degree of detail in a score ought to help the performer (as far as possible) grasp the composer's intentions rather than leading him/her "away" from things other than those intentions (if you see what I mean!)...
I am trying to define these intentions negatively rather than positively in the case of rhythm. If a composer writes, say, three levels of nested tuplets, then at each stage of the nesting one can fairly assume that he or she desires something
other than a regular or periodic pattern. What that might be could take on various forms, through the use of rubato, rhythmic stylisation, and so on. I might like to take this a stage further and suggest that a score is in general better understood in such a negative sense (rather than for communicating 'intentions', a term which may be rather too finite and as such insufficient to capture the infinite range of possibilities that a performer might bring to such a score).
If a composer writes as you illustrate here, it is indeed the case that something other than "a regular or periodic pattern" is intended, but when you then write about "rubato", for example, within such a context, I cannot help but wonder if such considerations might in some cases risk opening up a certain degree of potentially self-defeating "cancelling out"; what would concern me in an instance such as the one that you mention here is that the notion of wanting something "other than (xyz)" does not of itself mean "wanting something else" (other than what is literally notated, of course) and, when I look at a phrase incorporating three levels of nested tuplets (especially if further complicated by rests at the beginnings of and within some or all of these), I expect to assume that the composer wanted "just that" - i.e., that the notation should be telling me what the composer wants us to hear rather than serving as a mere example of "well, I don't want something other than that". By this, I also mean that writing a passage in such a way is not the only means whereby a composer can tell a performer that he/she wants something "other than a regular or periodic pattern". What also bothers me here is the extent to which the composer who obviously doesn't "want" to create, or even risk implying, "a regular or periodic pattern" in certain passages can actually tell whether his/her notated alternative to any such thing is sufficiently aurally perceptible to him/her and to the more adept and experienced listener.
I do understand that you are, as you say, looking at this from the perspective of the negative end of the telescope (if such an appallig mixed metaphor can be tolerated!), but again I do rather wonder if that very perspective may itself hinder rather than help our understanding and approach here.
Another slant on this pertains to listener attitudes, conscious and subconscious. In aural training classes at Royal College of Music years ago, I recall having to sight-sing passages from the two Webern cantatas and I have a dim recollection of a four-part passage in (I think) the latter which added up to the chord D-G-B-E moving stepwise to C#-F#-B#-E# (all from long distant memory and no score at hand to check), for which my tonally interpreted response elicited a horrified "but you shouldn't be listening to it like that!". Well, excuse me, but I recall no mention by the composer in a note in the published score that warned listeners not to allow their ears to lead them to read tonal assumptions into anything where none were intended. Not the most brilliant analogy, I admit, but at the same time by no means irrelevant as a kind of side-issue to what you write about here, I think.
Best,
Alistair
