01- You need some Ruby to delete all SectionPlanes:
This line of code + enter in the Ruby Console will do that:
m=Sketchup.active_model;m.start_operation('!');m.active_entities.grep(Sketchup::SectionPlane).each{|e|e.erase!};m.commit_operation
It's somewhat long as in includes code to make it one step undo-able.
It erases all SectionPlanes in the current context - so ones nested inside a group are not affected until you run the code inside an edit of that group...
02- As well as hiding other contexts completely during an edit session...
SectionPlanes can be assigned Layers.
That way you can assign different Layers to different SectionPlanes and switch them to be not visible in different Scene-tabs as desired: thus removing the visual 'clutter'.
Get used to using Layers, Modes, Styles and Scene-tabs in combination - you can have various tabs set up to enhance your modeling experience - e.g. you don't need textures and shadows on when making most 3d forms, and they will slow down orbiting etc, a tab to troubleshoot - with a Style set to show hidden geometry, color edges by axis etc is also a useful thing...