alt Hacker NewsParenthesis are for "taking a small detour from the current thought", either to add context or personal thoughts.
I use em-dash (written as "--" because I don't have an emdash key on my keyboard) as punctuation that sits between a semicolon and a period.
It depends on the goal of your writing. You can usually set off the same thought with a comma or a semicolon depending on sentence structure.
You can also just avoid the whole rigamarole and have a separate explanatory sentence.
Times change, good writers adapt.