If you're going to convert AC to DC such as in a battery charger or in the front end of a VFD, a three-phase six pulse rectifier will have significantly less ripple than a full-wave single phase rectifier which produces only two pulses per cycle. This reduces the peak-to-average ration of the DC current and the amount of filtering that may be required.
The minimum instantaneous output voltage of a 3-phase bridge rectifier output (without filtering) is 0.866 times the peak value, which occurs when two of the L-L voltages are equal. In contrast, the minimum instantaneous output voltage of a single phase full-wave rectifier is zero. And if you want even lower output ripple and reduced harmonic levels on the AC input current, with a 3-phase source you can have 12-pulse, 18-pulse, etc. rectifiers by using phase shifting transformer arrangements.