Mathias' reason resonates with me a lot and I agree with it completely.
It could also be seen as a purely aesthetic difference, but readability often follows from aesthetics, so one's stylistic choice can always matter beyond aesthetics.
There's also Douglas Crockford's famous quote about parens inside versus outside the containing parens: https://www.youtube.com/watch?v=taaEzHI9xyY#t=34m33s
Just like anything else with matters of style: be consistent within a codebase. Either always put them inside the parens, or always outside.