Repeating things to remind the readers of facts is a different issue -- I just spun that off into a separate post. This is an extension of Subtle Things #2, using adverbs, because many adverbs are in fact redundant once you use a more specific verb.
In general, you don't want to over-use words too much. We've all had situations where a semi-common word just happens to crop up three times in two sentences, and it jars the eye. It starts to draw attention to itself.* The danger then is in hitting the thesaurus too hard in the search for synonyms to keep from repeating yourself too much. That's its own problem: using the wrong word because you were so paranoid of using the right word again.
How much is too much? When does the thesaurus steer you wrong? These are judgement calls. Subtle things.
Redundancy also strikes in giving the reader information inefficiently. It happens a lot with actions involving directions -- see #1 and #2 below. These are attempts to be clear about the action, and there's nothing intrinsically wrong with that. But. IMO, it becomes a trust issue at a certain point. I'll explain more when I talk about the examples individually.
There's nothing grammatically wrong with the following sentences (all from Disciple.)
- Frida reached up to take [the baby] down and kiss his cheek.
- He slung [the severed head] and the envoy caught it in his belly, falling back onto his ass from the impact.
- His sword fell from his skeletal hand and he screamed, his companions screamed, and none of them saw Sir Rostislav coming.
- Anders touched the knot of kir it offered and knit it into shape, twisted it and pushed it into the sphere’s surface.
Well, okay, you can argue about my grammar but this post's about redundancy and repetition.
- Why is this a "trust issue?" It's not obvious, out of context like this: the baby is being carried by a rider, and Frida is standing on the ground beside the horse. If she's going to reach for the baby, of course she's reaching up. If she's going to take the baby from the rider and kiss him, of course there will be downward movement involved. Therefore, up and down are redundant, and I'm trusting the reader to know that. Because my readers are smart, observant people. If this were, say, the first sentence of the scene and there was no context, I would leave it as it is.
- Back, here is redundant for obvious reasons. If you're catching a high-velocity thing in the gut, it's going to be awful hard to fall any way but back. Don't insult your readers' intelligence. They are smart, observant people.
- Repetition for emphasis. Something horrible just happened, and I want the reactions to hit the reader for extra oomph. Plus, in my head the close repetition echoes that microsecond it takes to realize what just happened and react: the guy it happened to first, then those close by him. I'm thinking I'm going to also use this sentence in a post about long vs. short sentences. One sentence, or three?
- It is a very common word and it can put up with a lot of repetition. But this is a bit much, for my tastes. The third it is redundant. The first one refers to something in the previous sentence. This could stand some re-wording for clarity; I'll have to consider the whole passage for that.
How much is too much, for you?