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The book lists six variations on how to use 桂枝汤 to treat exterior patterns. To me, this pattern is akin to what you feel just before you go down with flu. It may or may not be due to an infection. In any case, depending on the medical state the patient is in, OR the symptoms he’s expressing…

1. Add 葛根: if “项背强几几” even though the patient has 桂枝汤-type signs like 汗出恶风.
2. Add 厚朴 & 杏仁: if the patient is also panting. Note you don’t use 麻黄 to treat the panting.
3. Add 附子: if the patient’s exterior is deficient but so is his primordial yang-energy. He ends up over-sweating, loses fluids and is debilitated.  The idea is to use 附子 to 补阳化气生津. You keep 芍药 because it works with 桂枝 to deal with the problem of weak exterior qi.
4. Take away 芍药: if “脉促胸满”.  Here’s a case of 胸痹（aka心力衰竭）, where 桂枝 would certain help treat 心阳气虚, and so we have that as the star of the show, with some supporting roles. 芍药 is not given a role here because it’s not needed to 缓急止痛，收敛 and what more, its cold nature isn’t too suitable. Note: To me this is like how to help a guy with a failing heart when he expresses these sign. We’re probably responding to these signs with 桂枝, but it treats more than the signs, it treats the underlying heart problem, which may have created these signs.
5. Take away 芍药, Add 附子: if “若微寒”. this is like a combi of the previous two variations. The co-stars now are 附子 and 桂枝, and note that these are the herbs in 肾气丸 that power up yang energy. The 中国中医药出版社 textbook believes that the patient needs to be very weak to warrant the use of 附子, and hence “微” means “脉微”.
6. Double 芍药 & 生姜, Add 人参: if “发汗后，身疼痛，脉沉迟”. Here, we have a situation where the patient loses too much from sweating, and is left weak and aching all over. Broadly speaking, 人参 is for the weakness, 芍药 for the pain and 生姜 helps 桂枝 in warming the system up, both in the periphery and in the stomach area.