Yes, it allows to focus on the verb: "io sapevo che non ero morto" feels like an objective, matter-of-fact statement, while adding the clitic object sounds like "I knew that I wasn't dead". It happens often while adding emphasis in speech to "break" the grammar this way. Now, this sentence is weird no matter the context, but a sentence you might hear is "Te l'avevo detto io di stare attento" (I told you to be careful); both the additional clitic and the postponed pronoun are there for emphasis.
Thank you!! V. interesting. Makes total sense. What I do still find confusing, however, is the difference between "Te l'ho detto io di stare attento" and "Te l'avevo detto io di stare attento" (the difference between passato prossimo and trapassato prossimo), seeing as both seem to be translated the same way. Why is the trapassato prossimo not translated as I had told you to be careful? Similarly, with the sentence "Lui è morto" is that all of "he is dead", "he has died" (which are admittedly quite similar but potentially different enough) and "he died" (which is very different). Thanks.
Italian and English don't agree on their conjugations much; despite the similarities, "lui è morto" and "he has died" are two different concepts, because the English present perfect is a present, i.e. it indicates now the result of something that happened in the past, while the Italian passato prossimo indicates something that happened in the near past (although as time passes it's slowly taking the place of passato remoto too). In the same way, the Italian trapassato prossimo is used in ways that the English past perfect doesn't cover, especially in speech. "I told you so" can't be translated by "Te lo dissi" but rather by "Te l'avevo detto", probably because it implies "before you went and tried it", and it can occasionally substitute for passato prossimo as a courtesy form (trapassato prossimo di cortesia).
Could you please elaborate this a little more? I'm not a native English speaker and these kind of subtleties elude me. Unfortunately I just can't grasp this logic although I would like to; in my mother tongue we usually operate with subordinated clauses separated from the independent clause with a comma (use of gerund and infinitive forms of verbs is very limited), so it doesn't really make a difference to me ...