The -I switch

• Suppresses mesh iteration numbers.
• Normally, this switch is used only when generating a Delaunay triangulation or constrained Delaunay triangulation with no quality assurance.
• Suppresses the output of .node and .poly files, so your input files won't be overwritten. (If your input is a .poly file that doesn't reference a .node file, then a .node file will be written.)
• Cannot be used with the -r switch, because that would overwrite your input .ele file.
• Shouldn't be used with the -q or -a switch if you are using a .node file for input, because no .node file will be written, so there will be no record of the added Steiner points.