Under Health & Safety Law all employees need to receive training appropriate to the tasks they are being asked to perform so for example, if you are being asked to use a piece of machinery then you need to be adequately trained in its safe operation, likewise, if you are being asked to be a nominated First Aider in the workplace then you should have the appropriate training.
For those seeking employment then the more work related certificates you can get, the more attractive you will be to a potential employers so, for instance, if you are looking for a job on a refinery then getting your CCNSG card beforehand would be a big advantage over someone who does not have it, likewise, if you are looking for employment in a food related job then getting you Food Safety Certificate would make you a more attractive prospect for a potential employer.