Salary sacrificing is where you pay with things in pre tax dollars. For most people in most jobs the employer has to pay fringe benefits tax on it, so unless it's something that is concessionally taxed (like motor vehicle, carparking etc), and unless they are on the top rate of tax, it's not usually worth it.

But the health system has some concessions and nurses are able to salary sacrifice up to a certain amount without the employer paying FBT on it, so many people pay their mortgage, credit cards etc with pre tax dollars and no FBT is paid. This is sort of an incentive to hospital workers which is effectively a bit of a pay rise without it costing the health system more.

Just be careful though, because while it doesn't affect the amount of tax you pay, it does impact things like some centrelink payments/family tax benefits etc and also repayment of student loans.

Hope that helps!