"Don't need it at 50" is working under the assumption the PLD's DPS is good, that they're with a group of DPS and healers who themselves know how to control enmity. In a 50 trial, where the DPS checks are already super outclassed anyway, and with a mixed bag of strangers, it's probably not a bad idea to have one in stance and one off stance. But I won't stay anything unless I'm plucking hate out from under the tanks who are in DPS stance and getting pummeled on my non tank job despite spamming Diversion.

Do you need it? No, a tightly oiled group of folks will be fine. Is it still a good idea? Yes, if your healer died cuz they pulled hate.