In a number of situations, you may be required to go for a police check and it usually depends upon what job you are seeking together with what part of the world you may be from. In the majority of cases, you would be asked to go for a police check when you are seeking employment in an institution which looks after or trains vulnerable individuals such as children and the elderly.
But these are not the only reasons you might be required to go for a police check as the vast majority of security related jobs do also require that you get a police check done. For example, if you would like to seek employment at an airport then it would be absolutely necessary for you to go for a police check so that your background is satisfactory enough for you to be able to take up such a role.
Similarly, if you are looking to become a security guard with any company or organisation, you would be expected to have a proper security check which would involve a police check as well as a complete background report. You can usually get a police check through law enforcement organisations which might have local offices however it can also be done on the internet.