I think dysoni is not asking "What do you need Tungsten for?", but "Why do you only want to collect Tungsten in particular?".Go to Inara -> Engineering -> Componnets and select Tungsten.
From that list, take your guess. The stuff is used in a lot of premium synthesis receipes as well as a lot of high end heavy duty engineering. I need it (a lot) for heavy duty hull reinforcements.
Answer to that question is in OP post #13, where he explains: "I am full of everything except a bit of tungsten and so wanted to use it as an excuse to fly around and land on a planet and challenge myself with getting used to it all again."