Triathletes generally attend Master's Swimming classes to improve their technique or speed. From 2 to 3 times a week is typical, then the rest of the time is spent cycling or running. The vast majority spend one day a week either doing a long run or long ride, but what about a long swim? If you are racing Iron distances, you will likely develop lots of speed going to Master's classes, that is, unless you start having shoulder issues from all the speedwork. The Master's classes I've been to and watched the last 15 years spend little time on technique and a lot of time on interval work. Too much speed will lead to overuse injuries, which is compounded further if one has poor stroke mechanics. One thing I have advocated is the long swim with all my athletes--which they do not get from a Master's class.
The long swim lets the athlete tone down the pace while working on upper body endurance, as well as a chance to think about their technique. This goes further even when you break a triathlon down to the most logical aspects of analysis. So many have a weakness in at least one of the sports. They all are linked together through the day, especially in Iron distance. If you want to run faster marathons at the end of the Iron day, cycle more. Why? Because getting off the bike fresher will result in more "gusto" left for the run. Same thing goes for the bike, if you want to enter the bike portion not feeling like you just swam 10,000 yards, then you need a long swim. Sample sets (all freestyle): a) 6 x 500 with 1/2 min. rest. b) 1 x 4000 straight. c) 2 x 2000 with 1 min. rest. d) 4 x 1000 descending with 1 min. rest. e) 2 x 1500 broken to slow, moderate, fast each 500, with 1 min. rest. One long swim session per week should be incorporated into the plan to ensure you can get onto the bike without a high degree of fatigue.
The other aspect of this long swim is to train the mind to lock onto the body's tempo, so you know what that feels like. It should be steady sustainable pace that builds upper body endurance that a Master's class usually doesn't. Another benefit is you get the workout done quicker, because you're not sitting around waiting for the clock so much. Most of all, it breaks up the routine of hammering out lap after lap at max speed with someone tapping your feet every few seconds like you would in a crowded Master's class. Give yourself a break and start using the long swim to become a fitter swimmer with less shoulder issues--work on the endurance and technique at the same time.