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You should never have "filler text". Stepping-stone scenes, that ones that lead from one key scene to the next, should be necessary to the story in general and part of the cause and effect trajectory. If you use them for character building (showing the reader who they are rather than finding out for yourself), then all the better - just as long as this isn't the only reason for writing the scene.
If you add text to a necessary scene or throw a bit more light on a character, then it's not filler text as long as it isn't putting the story on hold while the reader wades through it. The golden rule is to keep the story moving, although you should let the pace slow after an scene containing intense or fast flowing action to allow the reader to 'get their breath back' so to speak, and to consider the implications of the previous scene.