Use the resistors at both ends. If you don't you'll end up with standing waves over the cable, a phenomenon that is better known with radio hams than with PLC users. The damage that can be done depends on the frequencies in use, the length of the cable, the place(s) where equipment is connected and so on. It is very possible you have never had any problems so far, but the moment all conditions are at the worst, you'll be convinced to use terminating resistors for the rest of your life, believe me. And don't think it won't happen with DH+ because of the limited frequencies. Don't forget to take into account that these signals are digital and therefor you need to count in also the harmonics.
Kind regards,