Your MacBook supports USB Target Disk Mode when you use it with a compatible, full-featured (“super speed”) USB-C cable. Note that the USB-C Charge Cable (included with MacBook) does not support USB Target Disk Mode.
Probably nothing.
To elaborate: USB-C has 24 pins and looks like up to 18 conductors. That's power, ground, more power, four shielded differential pairs, an unshielded twisted pair, and three special function wires. A full cable is going to be thicker and stiffer than one that just has enough to support charging. The user experience of a thin, supple charging cable is going to be different from a ticker, stiffer, superspeed+ cable.
