I use it after cleaning the impeller on my aquarium filters. They naturally collect goop around the magnet bit of the impeller which makes them quiet, but eventually there will be too much goop and they stop spinning or make a horrible racket. If you clean it off all the way it will buzz and rattle for a while. A big blob of vaseline will quiet it down until the goop builds back up.
I haven't noticed that yet. A lot of the goop is from decayed duckweed and poo debris getting jammed near the impeller. Might take 3-6 months for the impeller to get stopped by the goop. Vaseline isn't a very good long term lubricant for aquarium impellers because you'll open it up a week or two after being applied and sometimes it will be gone (probably sucked out and globbed somewhere else inside the filter). Really good temporary solution though.