I have a question regarding the economizer in climate zones 2a, 3a, and 4a. Per ASHRAE 90.1-2013 Table G3.1.2.7, no economizer is required for the baseline model for HVAC systems in the climate zones mentioned above. However, per Table G3.1.2.8, the economizer high-Limit shut offs for climate zones 2a, 3a and 4a are 28 Btu/lb.  
If no economizer is needed for climate zones 2a, 3a, and 4a, why has the economizer high-Limit shut off been required for the economizer in these climate zones?