Those who swim in the heats but not the finals still win medals if their team makes the podium. The tactic does not always work, such as when the British 4x200m women's freestyle team missed out on the Beijing final.
However, the US, Australia and Britain have depth and substantial Olympic budgets. New Zealand's funding is more finite.
The crunch for the Kiwi relay swimmers will come early. The Games pool events are on the first eight days of competition. The women's 4x100m freestyle relay is on Saturday, July 28.
Eight of the 16-strong New Zealand team are at the Games solely for relays. They are Tash Hind, Amaka Gessler and Penny Marshall (4x200m and 4x100m freestyle), Samantha Lucie-Smith (4x200m freestyle), Carl O'Donnell (4x100m medley), and Dylan Dunlop-Barrett, Steven Kent and Andrew McMillan (4x200m freestyle).
It is understood the race-off situation was reiterated to team members at the camp in Cairns last month to minimise complacency.
The SNZ selection criteria includes the following Performance Requirements clause: "SNZ philosophy is to ensure the best possible relay team is on the blocks representing New Zealand at the Olympics. Selection by the NZOC for the relay team is no guarantee of swimming in the relay event at the Olympics, as the final composition of the team will be determined by the coaching staff at the Olympics and may include swimmers selected for individual events who are not selected for the relay team but whose performance at the Olympics warrants inclusion within the team. The selectors may require all available swimmers to demonstrate their fitness either through an individual event or time trial at the Olympics."
The Herald on Sunday has been told the relay most threatened by change is the women's 4x200m freestyle. Six have been named - individual 200m freestyle competitor Lauren Boyle, Hind, Gessler, Lucie-Smith, Marshall and Melissa Ingram. They finished in that order at the national championships, the main selection tool.
However, Boyle will compete in the 200m and 400m freestyle over three days before the relay. Her 800m heat is the day afterwards. There is a suggestion she could be rested but, as New Zealand's fastest in the discipline, that would limit the country's chances of progressing past the heats. The other alternative could see a race-off for selection, although Boyle and second-top qualifier Hind are expected to be safe.
Three-time Olympian Helen Norfolk, now the swimming representative with the New Zealand Athletes Federation, has no problem with late relay trials. She competed in New Zealand's 4x200m freestyle team at Athens and Beijing.
"You want the fastest team at the Games, so no relay place can be set in stone. No one can have an easy ride to the Olympics. For instance, I think it's great New Zealand has such depth [in the women's 4x200m freestyle].
"It might mean you strike Melissa Ingram [who broke Norfolk's 200m freestyle record] at her best and the team will perform better at the Olympics as a result. The race-off will also get rid of a few athlete nerves, because they'll know they're at their peak for the Games."
In the men's 4x100m medley relay, Matt Stanley (who will compete for New Zealand in the 200m and 400m freestyle after breaking Danyon Loader's 16-year-old records in March) could challenge Carl O'Donnell for the anchor leg.
In the men's 4x100m medley, Daniel Bell earned his place with the fastest butterfly time in the Olympic qualifying period (53.57s) but, if a race-off is allowed, Andy McMillan (53.78s) could test the system.
No changes are expected in the women's 4x100m freestyle or men's 4x200m freestyle but the selection clause means it is at the coaches' discretion in London. Mark Regan is team coach, with Scott Talbot, Gary Hurring and Jeremy Duncan named as assistants.