"If you blow air into your bobbin case then you'll never know where the lint will go to and it can ruin your machine."
I'm not so sure about that. I know that with older machines that just isn't true. The basic sewing machine is pretty simple. All you have to do is open up the bottom tray of the machine and there they sit at the bottom, all of those little dust bunnies, patiently waiting to be released. Even if they did get "brave" and mingle with the machine parts, it's a dust bunny against a big, tempered, steel rod...no contest.
Now, I can't vouch for the newer, fancy machines. Maybe the dust might affect the computer workings...I dunno.
~C