At it's heart, that's what planning is, right? The more planning you put in, the easier the execution yes? Well, one of the outcomes from planning good fiction is better and clearer reading.
Well, better reading is totally up for interpretation of course, but clearer! Ah, now there's a word that is, by definition, unambiguous! Make no mistake: as authors it is our job to tell a story, and anything standing between you and the reader that hinders that should be removed. And that includes our own tendencies as writers to indulge ourselves (ie. purple prose) or, for all the best intentions, simply try too hard.
I'm gonna set you off on a little quiz now. Right now, off of the top of your head, how many different words do you know for 'said'? Give yourself a minute, then keep reading.
So, how did you get on? Ten? Twenty? What words did you come up with? Off the top of my own head, I can think of: replied, spoke, sneered, quoth, cried, screamed, retorted, snapped...you get the picture.
Now, in some circumstances, using these kind of words in place of 'said' is just fine: they're like a spicy version of 'said'. But just like spices, if you use them too frequently you're going to clutter what your reader is attempting to savour. Either that or your reader wil watch in fascination as you attempt word-jenga with yourself, watching characters crying, quothing, declaring and responding all over the place, wondering when it's all going to come all crashing down.
And this is all because there is a fear among new novelists of that word 'said'. And it is a fear that your readers do not share or care about. Oh, you may think that the word 'said' is bland and boring, but that's the point: the simple fact of the matter is that the word said - and perhaps 'asked' and 'replied' - are perfect for your reader because it is so bland and boring. It is a transparent marker that points out, as unobtrusively as possible, who is speaking.
As I said, sometimes using those spicy versions of said (known as 'said bookisms' in the business) are are fine and can in fact add a dash of exciting flavour to your dialogue. I know that some editors out there despise said bookisms but I as a reader do like a good sneer or growl now and then. But they must be used sparingly, otherwise it, like purple prose, will draw the attention away from the dialogue itself onto these markers which sould be as clear and unhindering to the reader as possible.
Worried that you're not being exciting enough? Don't be; if you're doing your job as an author well, the story itself should be the excitement, not these technical points. If you rely on said bookisms it just looks like you're trying to cover up a weightless story.