Time trials are great - one boat, with competitors taking turns running the same course on it. Providing there's no change in wind and/or current, you'll get the most even playing field...but really, nothing is quite as exciting as head to head competition.
Having your competitor in a boat right next to you, trying to beat you,
not only adds to the excitement, but it makes for faster course times
from almost all rowers.
In a time trial: he'll give it his all,
and you'll give it your all,
but head to head, you'll both give a little more.
In the end, we all have a little more fuel in the tank than we thought we had.