Hi Pbacot, hi folks.
From the chapter devoted to concept in the SketchUp (SU) User Guide (UG), you can read:
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Layers
SketchUp layers are used to control the visibility of geometry within large models. A
SketchUp layer is an attribute with a name, such as "Layer0," "Layer9," or "Chairs."
Elements can be assigned different layers. For example, all Component entities that
are chairs can be assigned to the "Chairs" layer. This layer can be then be hidden temporarily
to hide everything on the layer from view.
Note - Geometry on one layer is not separated from geometry on
another layer. For example, faces sharing a common edge will both be
affected by a modification to that edge regardless of what layer the faces
are on.
Default "Layer0"
There is one Layer, Layer0, in SketchUp, by default. All entities are automatically
placed on this layer unless you create another layer, designate the new layer as the
active layer, and create entities on the new layer.
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And further down in the same chapter, you can read:
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Layers, Groups and Components
Layers are a mechanism for controlling the visibility of entities within a model. Entities
can be assigned to different layers in a model and those layers, and their contents,
can be displayed independently. Groups and Components are used to isolate geometry
as sub-models within an overall model, such as a component of a chair within a
model of a room.
Note - Entities within a group or component can be on several different
layers.
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I also suggest that you read the entire chapter devoted to the Layer Manager.
Just ideas.