Reference images don’t zoom, so if you’re doing very detailed, precise work to a reference it can be easier to put reference on a plane, then you can zoom in (in orthographic mode) to do details and reference zooms as well.
Very narrow tubes can be used to create “lines” in 3d space. If you need very precise, complex edges (curving hard body like a car for example) you can define these edges with tubes, then use them as guides for creating the surfaces that lead up to them. The tubes aren’t part of finished piece, they are just guides.
You can see some hard surface things I’ve made here