I have to disagree (I haven't read this entire thread, so apologies if someone else has already pointed this out). Having the pre will allow you to push signal through long cables with less loss, most noticably in the high end. This also means that your tone is consistent through basically any cable length.
I have run pres flat vice turning them off myself. Some might say what I was hearing was a baked in high end, but the phenomenon I'm describing is backed up by the theory, the pre reduces your output impedance, which lets the signal be less affected by the cable impedance.