They help you give extra information in the MIDDLE of a sentence. For example:
Cats - a common pet
Cats (a common pet
Cats, a common pet
If there are commas in your extra information, use "()" or "--" not ",,"
This is a common problem with keyword lists.
OK: The three disadvantages - A, B, and C - that this causes are a problem.
OK: The three disadvantages (A, B, and C) that this causes are a problem.
NO: There are three disadvantages