Any parents on Southperry? Guessing .. no

I mean his wife might not have milk when the baby is hungry, the milk doesn't come on demand/there might not be enough. So sometimes you have to use formula.

The milk does come on demand. Rather, in the first few months, it is produced continuously. The baby's suckling is what determines the rate of production. If there "isn't enough" (meaning it's not produced fast enough for hungry baby's liking), the cure is not to give formula. It's to keep the baby suckling until there's more.
You only have to give formula if the baby is showing signs of dehydration - and that should not happen when it is latching on correctly and Mom is not starved or severely dehydrated herself. The cases of true organic flaws that make a woman unable to produce enough milk for her baby (or twins, for that matter), are very few. Ignorance is a far more common cause of "not enough milk".

Edit: Before I get tagged as a breastfeeding fanatic (too late?), let me say this: If you choose to formula-feed your baby, that's ok. As long as you don't do anything stupid like over-dilute the formula in an attempt to save money, your baby should grow up just fine.
However, breastfeeding is better. And if you choose to do that, you should get informed about it so you are not forced to quit earlier than intended.