It is desired for the production version of a board to allow for boundary scan JTAG operation by default. If needed for software debugging the JTAG_MOD pin will be tied low. This requires leaving the JTAG_MOD pin floating or tying it high. The hardware manual states for normal operation tie the JTAG_MOD pin low. However, it doesn't define what is normal operation. If the JTAG_MOD pin is left floating, will the chip boot and run correctly?
This is a MCIMX6D6AVT10A. However, I think the question is fairly model agnostic.