HCG during a cycle will maintain testicular size and function and prevent testicular dysfunction. It should also be noted that administering over "500ius will cause an increase in estrogen and progesterone, but levels under this are manageable along side the higher Test levels with an AI.
Also keeping the function of your testicles will help recover and will aid a smother PCT which would be a better approach that the cure of testicular dysfunction at the end of a cycle and prevention would be a easier way by using HCG during a cycle imho. Dr.Crisler mentions it often in his PCT protocols and quotes many studies Ronnie.
I guess use what works best for the person but I would advice during a cycle better than at the end IMHO.
congrats on the book mate