Pacing is a good part of moving the plot forward. Just stringing scenes together doesn't make a story. There needs to be a way to get from one place or one time to another. Transitions are a way to do this, but how to do this without bogging the story down. The rhythm of a story is important and rhythm is the pacing. Knowing when to slow down or when to speed up is an art learned and mastered with practice.
Running one scene into another with nothing to connect them makes for a jerky ride when a smooth one will keep the reader going. Transitions are a way to help this process. A transition can be a single sentence that leads the reader to the next scene or it can be a lengthy passage that summarizes time to move the reader and the characters on to the next scene.
So how do you choose what to use as the thread to pull the reader from one scene to the next. You could choose to stay with the same character. This can work but what if you need the next scene through another character's eyes. You need to find perhaps a word, a phrase that can be repeated to start the scene. You could use the same setting. No matter what you choose, finding that thread and using it will pull the reader forward.
Another thing about transitions is often they're telling and we all know the rule, show and don't tell. Sometimes telling is the only way to more the story forward and sometimes it isn't. Finding a balance is important. And knowing if what the reader needs to know deserves a scene or just a bit of summary.
Transitions are important to the pacing of a story. Learning how to use them can help build a better reason for the reader to continue reading.