security clearances are many levels - to determine if a person
can handle/see certain levels of information.
Some information may seem trivial - but accumulated over
time/different people can form useful intelligence that some
countries/people are interested to use against Singapore.
As to how/why a person is granted a certain category, its
classified - official SECRET. Nobody who really know will tell you
how/why someone is a certain security clearance.
No matter what - all official matters to do with civil/govt
service are on a need-to-know basis. It doesn't mean if a person is
cleared a certain level, he/she can see everything....only if it
pertains to the person's necessary work.