Pre post effectos is a crucial factor for signal clarity. A general rule that I believe most will condone is to put it in as pure as you can, then mess with it later giving it the shortest path possible. For obvious example if you (taboo) pre effect a phase shifter on a signal and it is recorded as such, that's it pal, you're stuck with a phase shifted signal recorded. period. You cannot undo a 90 degree shift by going back to the previous 270 degree mark. hehe no that wont work. same goes with CHOR FLAN ECHO (exc. pure delay) and just about any invasive or combination of effects that include an invasive one in it.
I have to even include EQ extraction to a certain degree, as it changes clip points and always raises the noise floor. (that's not good)