They vary widely in effect in my experence. If I didn't have a problem I would leave it off,I do: if the woofers flap wildly then use it. It does have an effect on the bass but if you need it you need it. One of my phono stages has both RIAA and IEC {?] curves; the latter rolls off the bass more. See which works better on your system, off or on, and go with that.