My Five Point System for Deciding if Something Belongs in a Manuscript
This system was mainly devised for me to be able to decide whether or not to include a scene in a manuscript, but it would work for just about anything, such as a sentence, an object, a character, a piece of dialogue, etc.
1.) Is it important to the plot? In this instance, you're asking yourself if the information/whatever is important to the progression of the plot overall at that spot. If the answer is yes, include it. If no, continue to question 2.
2.) Is it important to the development of a character? Does the character grow/change because of the occurance? If yes, include it. If no, continue to question 3.
3.) Does the reader need to know the information to progress to the next chapter adequately? If your character, Jimmy, sees his girlfriend, Sally, kissing his best friend, Rick, in your problem spot, and in the next chapter confronts Sally and/or Rick about it, then it's likely you need to include it. This is, of course, a simplistic example, but you get my meaning. If all this is true, then include the scene/whatever. If no, then move on to question 4.
4.) Will you be able to use the scene as a jumping off point for a subplot later in the manuscript? Sometimes the things we add to a scene can lead to amazing revelations later, such as the vase that got cracked in chapter 5 might become a focal point in chapter 16 when it is realized that the treasure map is actually hidden between the layers of the pottery. If the answer to this question is yes, include the scene; if it's no, continue to the final question.
5.) Does the scene/item/sentence/whatever speak to you, the author, in some way? If it does, it's likely that it will speak to readers in the same fashion. This is one of the "fall back" circumstances of writing: It's just too good to cut out of the story. However, it should not be used as a "catch-all." Sometimes, bits and pieces that we think are wonderful and *have* to be included really don't contribute in any significant way to the story as a whole. Example: If I wrote that Tabitha had a pet bird that sung Garth Brooks' "Friends in Low Places" to her every morning, but the fact didn't have anything to do with the fact that she's in hiding from the law, well, it could be included because it shows something of Tabitha's life. But if I were to say that Tabitha liked butterscotch puddings on Sundays and go into no further explanation, then it's merely filler information. Nothing that is included in a book should be "filler" in the sense that it's there to take up space. The difference between filler and transition pieces that move us from one scene to another is that when it's filler, it just seems "out of place." When it's detail in a transition, it usually speks to the character's personality or emotional well-being.
I don't know if this will help anyone, but I have used it, and it works for me.