The Power of Minor Characters & Stage Directions

I personally think there are way too many minor characters within Macbeth. There are some who are only in one scene and there are some who only have one line. Still, are they relevant? One in particular who only happens to have to lines is Seyton. There is no coincidence that his name resembles Satan so closely. But who is Seyton? He only appears for this one scene within Act 5 and he is not mentioned anywhere else within the text. Why is it that Macbeth calls out and summons him right before the death of Lady Macbeth? Could he have played a part in her death or was he simply called to collect her evil soul?
Another interesting aspect of this scene is that it is different depending on the version of the text you are reading. I know for my version of the text there are no stage directions for Seyton besides when he enters after he is summoned by Macbeth, still he somehow knows about Lady Macbeth's death. It is mentioned in the footnotes of my text that in other versions of the text a servant comes in and announces her death, while in others it is said that Seyton exits and re-enters. I wonder why editors take it upon themselves to alter various aspects of the text. Also, is it really adding to the text or merely sucking out the eery feel to this entire play? I think that it is important to keep the play how it was intended to be presented