Ok, I have searched previous posts, found several references to setting the timing to 12 degrees BTDC, but no explanations why one would do this on the Xterra, "just because".

Can someone explain why one would wish to do this? I have seen reference to it when people list "mods" for their X and would like to know what, exactly, that is does to increase performance.

It doesn't seem like something to do unless you have made modifications to the engine, i.e. cam, blower, exhaust, fuel system mods, etc.

Just curious.