It can group parentheses together like how parantheses group numbers.
In a problem like this:
2[ x + 5 / (4 - x) + 6(3x) ]
Parenthesees and brackets mean the exact same thing.
It is just easier to see and understand when using a different-looking symbol instead of putting a bunch of sets of parenthesses inside each other.
But if you are talking about in interval notation,
brackets mean "inclusive" and parenthesees mean "exclusive."
The interval [ -5 , 8 )
is all numbers from -5, including -5, up to 8, but not including 8.