With a one bonus point win advantage on the points table after South Africa's loss to Australia last week, the All Blacks did not want to lose that buffer. But they needed to keep vitality and also get players back from injury into their selection mix.
"We know we had a good win last week and we know expectations are high on us, and the danger is if we think it is all just going to all happen, then we are going to get smacked. So there's a lot of pressure on this group," Foster said.
"We've got to make sure we have a really good performance this weekend and, from a Championship perspective, this win is vital for us.
“It's part of the challenge of being an All Black. You've got to prepare to play and whoever puts on that jersey, we've still got to be responsible for the performance.”
Foster said the six-day turnaround and five Tests on consecutive weekends meant it was important to use the energy across the group.
"Some of these changes are people who played significant minutes last weekend anyway against Argentina," he said.
It was a situation the management had flagged, and it would be something each of the teams would be dealing with during the Championship, he said. It was also a reflection that they were getting experienced players back from injuries.
Foster said while it was important to give younger players opportunities, it was pleasing to do that with experienced players around them.
"It gives us the confidence to get that blend between making sure we've still got experience on there," he said.
Foster said first five-eighths Damian McKenzie has a clear understanding of his role in the Fortinet Rugby Championship. With only two first five-eighths specialists, it was a common-sense choice to manage Beauden Barrett for the South African Tests.
But he also saw it as a vote of confidence that McKenzie was progressing in the position.
Hoskins Sotutu returns at No8. He was a highly skilled player, and the selectors had talked with him about the work rate they needed from him in the physicality of Test matches.
"The reason he's in there is he's been training well for us, he's contributing well off the park and, again, he's got a huge desire to go out and start to play. We're looking forward to seeing how he goes," he said.
Rieko Ioane was playing at centre, although Foster said their preference would have been to play Anton Lienert-Brown, he wasn't quite ready to be considered after his hamstring tweak ahead of last weekend's Test.
"He's on top of his game, he's fit and keen and so it's a bit of a workload for him but, again, he's thriving on wing or centre," he said.
Tighthead prop Tyrel Lomax had impressed off the bench last week. It had been tough for him with each of the tightheads in the group playing well, he said, and it was a good chance to give him a start.
"He's a good scrummager," he said.
He showed his ability in dealing with the different tactics the Argentinians employed at scrum time, Foster said.
"I was quite pleased with the way he learnt, adapted and adjusted to that and around the park he's on the balls of his feet bouncing around and looking to get engaged in that ruck and tackle area so we were pleased with him and are looking forward to seeing him in a starting role," he said.