Please refer to page nine of the Sharp [S108T01 / S108T02 datasheet](http://media.digikey.com/pdf/Data%20Sheets/Sharp%20PDFs/S108,208T01.pdf):

![enter image description here](https://i.stack.imgur.com/coRqa.png)

Is this diode needed - why/why not?

How do I choose the correct diode, if yes?

UPDATE: Thank you all for your educational inputs. We've decided to go with the diode since it will not add significantly to the cost of our product (a vaporizer) and this will keep it on the safe side, right?