The ACN Maps are designed for use with californias specific blend of fuels. because the legislature in CA seems to think that lowering the carbon footprint of fuels will magically cause less pollution and rainbows from exhaust pipes. politics aside states with CARB standards like CA will have more "environmentally friendly" fuels and even at the same 91 mark will provide less knock protection than the same fuel from the same station across the country. * especially in Winter time when CA is transitioned to much dirtier/less combustible "winter blend* the ACN maps typically run lower boost to prevent knock with lower quality fuels.
Some drivers get away with using the standard maps but they created the ACN map for a reason. the consensus seems to be if you run the OTS 91 map and when you log everything looks good (read knock protection, timing, AFR correction) then keep using it, if you see alot of knock correction then you should switch to the ACN map.
And as always, use top tier fuels from reputable pump stations
13 WRX Hatch - Cobb OTS Stage 1