That's the question, I suppose. Hamlet has been performed with them completely removed, and supposedly "no one knew the difference".
I'm an English Lit major, and I was told that everything in a great work of literature is there for a reason. I've read authors write about writing and written myself since then, and now I suspect that's bullshit. You write what works and sometimes, by chance, something beautiful and symmetrical comes of it. Of course, I'm a hack and terrible writer, and they could have lied. I suspect the answer is probably in-between... great works of literature work because there is so much to find in them, but it wasn't necessarily put there by design...
So, maybe there is a bit of that English Lit major in the question:
Why did Shakespeare feel it necessary to create Rosencrantz and Guildenstern? Were they just just a knife and fork to feed Hamlet his lines?The answer might depend on the interpretation of Hamlet's relationship with them you (or the version of Hamlet you see) choose. In AP English class I was told they were aquaintances, sort of like kids Hamlet was in the same class in school with. I saw and see no textual evidence for that. Nor do I see any textual evidence that they were even necessarily going to Wittenburg with Hamlet (though I might be misremembering). Based on what the king and queen say to them, I'd say their parents were probably favorites of the old king Hamlet. They were brought up at court together, playing together as children often do with others of the same age who happen to be around. Not best friends, but not just "in the same class".
There are varying readings of his initial greeting of them as well... some seeing genuine affection in the greeting, other seeing him treating them like shit from the get-go. Its a tossup really, but for the sake of argument, lets say Hamlet is genuine with them until he gets suspicious.
Now lets back up for a moment. Think of how he treats Ophelia. I recently read a criticism that suggested that his ill-treatment of Ophelia was triggered by his anger at his mother. We don't really believe that Ophelia is a gussied up trollop, do we? He was angry at his mother and by extension all women... Staying with me here?
Why was he angry? He was a being a bitch to be around before he saw his fathers ghost, and the feelings he expresses are echoed in his madness (pretended or real). His father died and life went on. His mother remarried, and the people accepted a new king. A double blow.
Both should have shown more resistance by Hamlet's estimation.
And now, his childhood friends, whose fathers were his beloved father's favorites are being toadies to the new king. As if nothing was wrong. Just as they were his friends because their affinity to his father, now they are his enemies because of their affinity to his uncle. And as far as Hamlet is concerned, they deserve what they get because they should have chosen their king more carefully. Just as his mother should have chosen her new husband more carefully.
Nevermind that they didn't personally choose him, they are obviously taking his side. Just like Ophelia.
In case I'm not being clear (and I might not be, I'm getting myself riled up), I'm suggesting that Rosencrantz and Guildenstern are to the courtiers/people as a whole, as Ophelia is to womankind as a whole in Hamlet's eyes. That his actions towards Ophelia and RosnGuil are parallel of the same kind of anger that his uncle was accepted as a substitute for the great man that the old King Hamlet was.
How dare she? How dare they? He can't whip himself into a frenzy at his mother, so he does to Ophelia. He can't berate the court as a whole, but he can his friends.
Not a perfect theory, but its one I've never read anyone else postulate... though I'm sure someone somewhere has put it much more eloquently, with neat little footnotes and citations.