In case you're not sure what touch typing is, it's typing without having to look at your keyboard. By your touch alone (and some muscle memory).
Assuming you're a programmer too, here are two articles you must read:
If you din't read those, this line sums up Jeff Atwood's post:
What I'm trying to say is this: speed matters. When you're a fast, efficient typist, you spend less time between thinking that thought and expressing it in code.
Let's say speed doesn't matter to you. You still want your typing to be as spontaneous as writing. You don't want to think about pressing the right keys (just like you don't need to think about writing every single letter the right way).
Touch typing is super easy. All you need to do is practice for about 5 - 10 minutes everyday. And once you get it, you won't be able to imagine work without being able to touch type.