I'll start, but perhaps my colleagues from Finance can jump in and help as well.
There are two real objectives the WITB serves to address. First of all, as you mentioned, it helps encourage people to enter the labour market. But it also has a second benefit, which is to reward those people who are already in the labour market and are not earning a lot. They'll be topped up, which is very helpful for folks in those kinds of situations.
It's been designed so that you already have to be earning an income, and it tops up earned income. You can't just have a low income. You have to earn at least $3,000, at which point, for every dollar earned, you are given additional money, until you get to a point of $5,500. Single individuals would continue to get the maximum benefit of $500. When you earn over $9,500, it's reduced at a rate of 15%. It slowly reduces the amount so that by the time you earn over $12,800, you receive no more benefits. This is for singles.
It's a little different for families, including lone-parent types of families. There's also a top-up for those who have a disability.