The function is documented in torch.Tensor.permute 480. Could you post some code where you think this might be a no-op?
Here is a small example using it:
x = torch.randn(1, 2, 3)
print(x.shape)
> torch.Size([1, 2, 3])
x = x.permute(1, 2, 0)
> torch.Size([2, 3, 1])

print(x.shape)