I've cut my business travel within the USA due to the variable time it takes to get through security -- on a good day I can breeze through in 20 minutes or less... on a bad day it can take 90 minutes or more. So to be assured of making my flight, I need to plan for the worst.

Even real-time security wait times are little help since even if it shows 20 minute waits 2 hours before the flight, an equipment problem or personnel shortage can make that wait much longer before I get to the airport.