But the effects of not going straight are nowhere as obvious (although invisible to spectators) as in the iron-distance swim. Whereas top competitors swim an absolutely straight line between buoys, the further back you go in the pack the more swimmers start looking like drunk drivers on a Saturday night cruise. Freestyling straight in open water is a challenge for everyone.
I always found that the one advantage of breast stroke is that you can see where you are going. So if your breaststroke is almost as fast as your freestyle, you may want to consider swimming breaststroke instead. Once you are out of the initial melee there is often plenty of lateral room for a good breaststroke. And what you lose in speed you will more than make up in distance saved.
Furthermore I would postulate that all improvements in swim time that age-groupers brag so much about, come from swimming straighter and closer to the optimal path, rather than from speed per se. The more comfortable a person gets, and the more experience they have in open water, the better the line they pick.
Going straight is also something triathletes should practice on the bike. Often "triathlete-geeks" incur the wrath of "serious cyclists" by wandering all over the road. And the more aero their position gets, the worse the wandering becomes. Nothing is as iconic as a guy zig-zagging all over the road in his aerobars at 12 mph.
On the bike, going straight and being predictable is about more than winning races or riding in packs. It is also the key safety measure and all cyclists should be taught and should practice riding straight. The more predictable a cyclist becomes, the less likely he or she is to die in a traffic accident. Weaving in and out of parked cars, swerving when looking back or grabbing a water bottle, and otherwise surprising motorists is not a good practice and one that you can pay for in blood.
Riding straight requires practice and nothing is better than a country road with good markings to acquire this skill. You should try to ride there (preferably when there is no traffic) and practice looking down, looking up, looking behind you, etc. while staying on the white line. It is natural for your body to turn when you turn your head. It is a built-in reflex and it requires conscious intervention to stop it. But nothing separates an experienced cyclist from a cycle tourist or casual commuter like riding straight and steady.