JavaScript: Why to put semicolons after each expression

By JavaScript standard it is not obligatory to put semicolons after each expression when there is only one expression on a line. Parser automaticaly puts it after line. For example:

var a, b
a = 7
b = 8

will be parse it as:

var a, b;
a = 7;
b = 8;

But not putting semicolons is not considered a good coding style and therefore sounds question: “why to put semicolons if it is not obligatory?”. The answer is that there are some cases that not putting semicolon breaks code execution flow or even worse – there is compilation error. I do not speak when there are two or more expressions, I mean:

return
true

this will be parsed as:

return;
true;

and undefined will be returned instead of true. Compilation error occurs, when jumping or breaking a label:

break
label

These are too simple examples, but there is shown why to put semicolons after each expression.