\b is a zero-width assertion. It doesn't match a space, or a character of some sort. It matches when a word character is found next to a nonword character.

Therefore, there isn't anything in particular to capture when talking about \b. So it's probably not really accurate to say that \b inside parens is meaningless, because it has just as much meaning as it would have outside the parens.

But that's the crux of it; position inside or outside of the parens is unimportant, in this case, because the function is identical. ...the act of relocating it inside the parens is pointless, because in or out, its function is the same.

Update: By the way, I ++ed the original question because even though it was pretty basic, it started out with "I'm sitting here reading the camel book." (paraphrasing)

Kudos to those who do a little homework themselves and come to SoPW for clarification rather than a spoonfeeding. Very good question, in that context.