What effects does the repetition have on description of the last stage of the man in the poem the seven ages of man?

It's not a poem. It's a speech. So you are best off considering how it will sound, because it is meant to be said aloud by a character in a play (the character Jaques in the play As You Like It, to be precise). Your question refers to the last line of the speech which is "sans teeth, sans eyes, sans taste, sans everything." The Word "sans" is of course French for "without". Try saying that line. You will find that you want to say it slowly, not trippingly. The repetition of the Word "sans" gives it more weight than it would otherwise have, so you end up accenting every Word and saying "Sans teeth. Sans eyes. Sans taste. Sans . . . everything." The last Word has a different rhythm which it sets it off from the rest and enables the pause before the last Word. The line is ten syllables long, as all blank verse is, but it is a series of strong syllables followed at the end by a dactyl (- - /). Had Shakespeare written this line as "No teeth, or eyes, or taste or anything." it wouldn't have had the same effect. Try saying that line. You will find yourself saying it much faster because it is a regular line of blank verse: "no TEETH or EYES or TASTE or A-ny-THING." That was not what Shakespeare wanted the actor to do. He wanted the actor to slow down.This slowing down effect complements the meaning he is trying to convey, best understood in the phrase from the previous line, "mere oblivion". The old man is fading away into nothingness. The repetition of the Word "sans" shows that this is happening bit by bit in little stages: first the teeth, then the sense of sight, then the sense of taste. Eventually, he fades away completely and is "sans everything". The repetition of "sans" helps us understand that this process is gradual and slow.This speech is a great example of why you cannot change Shakespeare's Words and expect it to still be Shakespeare. Shakespeare wrote his plays thinking constantly of how the plays would sound when spoken, and using the specific Words and rhythms he did in order to make the actor say them so they made more sense.