Yes, it is true that most students stick around from completing year 10 to go on and complete the HSC, though considering how many people I knew who dropped out in year 11 & 12, the School Certificate should still indicate completion of basic secondary schooling. These days, employers are in desperate need of labourers and trade work. If you didn't have any School Certificate, what have you got to show an employer that you aren't a completely illiterate individual? It helps to give an employer some idea of your education status, which is more current and accurate. It also verifies your progress reports from school, being able to compare them over time, as it'll reflect progress or deficiencies in certain subject areas...which will reach a climax for some at the School Certificate.