Fuel filters - why are there two?

[lpdsn]

lpdsn, I could effectively take the secondary out of the system by removing the element but some contributors to this thread say that would be suicidal.

I find it very handy to have two. For a start the usual CAV filters aren't good enough on their own, but also because my quickest response to a problem is to take off the pipe between the primary and lift pump and run the engine from a can - having a secondary means that diesel is still filtered. (You do have to allow for 90% of the contents of the can going down the return pipe to the tank unless you also bung the return pipe into the can.)