It stands to reason that reducing drag should be the first priority when aiming to improve your swimming times.
While the swim makes up a small percentage of a triathlon race, a lot of energy (both nervous and physical) is wasted in the swim that could be saved for the bike and the run.
Bobby Bowden
During the build phase, at least one technique-specific set is performed per week.
Advanced triathletes/swimmers have developed an optimal body position and have mastered rolling the shoulders through the stroke further reducing their drag.
Therefore these athletes would focus on improving or increasing their forward propulsion; this would naturally start with the “Catch” and “high elbow” entry type drills.