Those who make their own harness looms (crimp wire to Econoseal or WBO2 or injector recepticles), will probably want one.
This tool supports 3 wire sizes with it's installed head (removable head), the smallest jaw marked 0.5 .. 1 mm2 is suitable for Econoseal and JPT (WBO2, injector, and many other connectors). The biggest jaw is good for common size relay and fuse connections.