If you use it to clean a vintage machine it's just going to blow the dust off and out because they aren't encased. However, on newer machines it just blows the dust deeper into the casing.
You can use a piece of polar fleece, about a 1" square and a pair of tweezers. Just pick up the fleece with the tweezers and run it around inside the bobbin casing and any area where dust accumulates. The dust/lint will cling to the fleece. I usually keep a snack baggie of small pieces of this handy to use.