The general feeling is that if dialogue in a scene needs the tags, it's poorly written; that writers should aim for conveying emotion through the characters' words instead of spoon-feeding it to the readers in the narration. It is the mark of an insecure writer that he feels the need to give you information that should have been conveyed in the dialogue, to make sure the reader understands that his characters are emoting or what the scene is supposed to reveal. Trust the reader to figure out what the dialogue “means". And after having a couple of critique partners review it, if they point out that a run of dialogue really is too obscure, then take the time to re-write. Beats are easy to add where they are needed. It's harder to extract them, I find.
In the book “Self-editing for Fiction Writers" by Renni Browne and David King, the authors suggest:
“It's best to replace only a few of your speaker attributions with beats. A beat after every line of dialogue is even more distracting than too many speaker attributions. What you want is a comfortable balance."I tend to agree with that sentiment. Too many tags or beats in a run of dialogue can throw off the momentum of the scene so much that the readers forget what the characters are talking about by the end of the page!
I don't think that all beats and tags are bad. I do think a writer needs to choose her beats wisely and make the most of them. First she needs to understand the anatomy of the scene she is writing: What are the key emotions at play here? How fast is the exchange between characters supposed to feel? What else is going on in the scene? and Which actions are important to the development of the scene?
And now, because examples in real life are always fun, I'm going to borrow from J.K. Rowling to illustrate my point. What I love about Rowling is that she's not perfect. But her characters emotions are perfectly conveyed.
Excerpt from “Harry Potter and the Prisoner of Azkaban":
“I DON'T BELIEVE IT!" Hermione screamed.
Lupin let go of Black and turned to her. She raised herself off the floor and was pointing at Lupin, wild-eyed. “You-- you--"
“--you and him!"
“Hermione, calm down--"
“I didn't tell anyone!" Hermione shrieked. “I've been covering up for you--"
“Hermione, listen to me, please!" Lupin shouted. “I can explain--"
Harry could feel himself shaking, not with fear, but with a fresh wave of fury.
“I trusted you," he shouted at Lupin, his voice wavering out of control, “and all the time you've been his friend!"
“You're wrong," said Lupin. “I haven't been Sirius's friend, but I am now--Let me explain..."
“NO!" Hermione screamed. “Harry, don't trust him, he's been helping Black get into the castle, he wants you dead too--he's a werewolf!"
Excerpt from “Harry Potter and the Order of the Phoenix":
“There is no shame in what you are feeling, Harry," said Dumbledore's voice. “On the contrary... the fact that you can feel pain like this is your greatest strength."
Harry felt the white-hot anger lick his insides, blazing in the terrible emptiness, filling him with the desire to hurt Dumbledore for his calmness and his empty words.
“My greatest strength, is it?" said Harry, his voice shaking as he stared out at the Quidditch stadium, no longer seeing it. “You haven't got a clue... You don't know..."
“What don't I know?" asked Dumbledore calmly.
It was too much. Harry turned around, shaking with rage.
“I don't want to talk about how I feel, all right?"
“Harry, suffering like this proves you are still a man! This pain is part of being human--"
“THEN--I--DON'T--WANT--TO--BE--HUMAN!" Harry roared, and he seized one of the delicate silver instruments from the spindle-legged table beside him and flung it across the room. It shattered into a hundred tiny pieces against the wall. Several of the pictures let out yells of anger and fright, and the portrait of Armando Dippet said, “Really!"
“I DON'T CARE!" Harry yelled at them, snatching up a lunascope and throwing it into the fireplace. “I'VE HAD ENOUGH, I'VE SEEN ENOUGH, I WANT OUT, I WANT IT TO END, I DON'T CARE ANYMORE--"
He seized the table on which the silver instrument had stood and threw that too. It broke apart on the floor and the legs rolled in different directions.
“You do care," said Dumbledore. He had not flinched or made a single move to stop Harry demolishing his office. His expression was calm, almost detached. “You care so much you feel as though you will bleed to death with the pain of it."
These two scenes illustrate very different emotions. Characters in both scenes do a lot of yelling, but the timing of the dialogue is the key to the emotions in each scene. In the Prisoner of Azkaban scene, the urgency of the scene is conveyed by quick back-and-forth dialogue. If you remember the same scene in the movie, there are a lot of actions that the characters take (i.e. looking to and from one another; Hermione steps in front of Harry to shield him from Sirius and Lupin; Lupin reaches out to implore Hermione to listen). None of those actions are portrayed in the dialogue, because to add them, while giving you a physically more accurate description, would take away from the momentum of the scene. The readers can just as easily imagine the action as they read the dialogue.
In the second scene, from the Order of the Phoenix, the dialogue progresses much more slowly. The emotion in this scene does not come from a rapid-fire exchange (although Harry does do a fair bit of shouting), but from Dumbledore's slow and calculated responses. The deep feelings of regret and care for Harry that Dumbledore expresses come to light through his patience in allowing Harry the space to explore his own emotions. The pace of the dialogue allows much more room for beats of character action (all taken by Harry, a detail that is also telling...). But more than that, each beat has a purpose, shows the emotion rather than telling it (more often than not).
As a writer, understanding what your characters are going through and how they would respond to one another in a scene can mean the difference between capturing the readers' hearts and getting lost in the details. The right beats in the right places give meaning to the words spoken and emotions felt by your characters, allowing the reader to peek through the windows in their souls.