The issue the instruction manual talks about is if you have the trigger at half-cock and the safety on, and try to pull the trigger (without taking the safety off). It could cause damage to the trigger mechanism.
But, in my opinion, either use the safety and hammer fully cocked, or switch out for the decocker and use the DA pull as a 'safety'. Using the safety and the DA pull is redundant, and greatly increases the chances of an ND when you're lowering the hammer by hand. But that is just my opinion.