The advantage of parallel output is that it’s fast:
all the data is available in real time, all the time.
Disadvantages include bulky (and expensive) cables
and limited cable length. Most encoders come with
cables a meter or two long, but a parallel output
using differential output and shielded cabling can
be extended to 100 m using a thicker cable, at a
reduction in speed. Open-collector (sinking or
sourcing) outputs can go roughly a third that far.