Every story needs transition scenes just like topic papers need transition paragraphs. These scenes keep the pace up and help the reader go from action to reaction quickly and easily. Most writer's don't think about there transitions while they are writing and that's fine, but when you are editing a draft of your work, look closely at the transitions. Do they make sense? Do they follow the basic rules? Do they help your pacing stay tight?
What is a transition? Transitions identify place, time, and viewpoint character. You need a transition if you change any of those three. Yes, if you change the point of view character, it's a transition and you need to name that character as soon as possible. If the mood or tone change in your scene, it's also a transition.
While naming a character can be as simple as writing "said Jolene", time and place transitions can be written any number of ways. You can name the place, or describe the place or event. You can also mention the time or day or date.
Transitions can be narrative (telling), who did what and when. The rule is to show not tell unless you are using it in a transition. A narrative transition is an easy way to indicate change without making a transition into a scene itself and slowing your plot. For example if the most important part of your scene is the next bit of dialogue, then you can transition with "he showered, dressed and went downstairs. "So Frank, have you figured out the killer yet?" he asked." vs "He turned on the shower, grabbed the soap and stepped into the warm water. Smelling the fresh scent he rubbed the bar between his hands and lathered it..." If a description isn't important to the scene then keeping it short and sweet is best.
Transitions provide description, break tension, skip unimportant events or times, quicken the pace, change locations and POV characters, and can create or switch tone or mood.
In short, good transitions separate characters, tone, scenes and chapters to create a faster pace and tighter plot.