As bgritzut points out, they always do provide both numbers, but why? Here is how I would explain it: The all-items CPI, as you suggest, is best for measuring the cost of living, that is, the actual impact on people's lives. In fact, for that purpose, it is good to look not only at the seasonally adjusted all-items CPI, but also the unadjusted number (all of these and lots more are given in the BLS press release, to which a link is provided). The core CPI, seasonally adjusted, is better as a measure of the impact of US fiscal and monetary policy on the inflation rate. The reason is that food and energy prices are set in world markets over which the Fed or Congress has little influence. Policymakers can better understand whether their policy is too tight or too loose if they look at the core.