Etch is very useful If you would like to show a part number or design element (logo) and... on a sheetmetal part (not just sm part). In general this is made by laser and its name is laser engraving, but you can use high speed "special" tools.
Cross Break is very useful to give stabilty to huge sheetmetal surface. We use it tool to sheetmetal doors.
Sean has many examples too. Sean?
Yes, I use the "Etch" command quite a lot,....this has the added bonus of making true type text into actual geometry, in the flat pattern output file.
As Imre says, it's ethos is centric to the creation of laser marking, and creates a layer for such in the DXF.
"Cross Brake" is something I draw on from time to time, when forced to use large panel areas, that require stiffening, or harmonic reduction....I usually make a model of the formed version, and link a cross break version to it, for use in the draft file. As it's currently the only way SE will display the correct bend information, from the call outs text, when used.
Design Manager Streetscape Ltd
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I use the cross break command to get break lines to show up in flat patterns. But that is all it does for me because I have to make my own bend tables (another can of worms). The break lines do not create geometry that can be used or seen. The break lines them selves can't be seen in Iso or 3D views in general.