Tuneman
If you are a sell side derivatives trader, whats the point of knowing how to price options? You are assuming that they are fairly priced, right? Your job is to simply buy or sell them for this already known price, right? So I am wondering where that knowledge comes in handy.
As diegmat says, the big assumption there is that you assumed it was fairly priced. If you make that assumption, I will happily trade with you all day!
You need to know how to calibrate your models, how they price so that you know what the second derivative of your product is (see all the greeks on options). You need to know how you can strip a product into component parts to sell it, you need to work out cross-correlations of what you are holding.
Ultimately, if your ass is on the line, would you let someone else build the tools you use without checking them and knowing them?