This is a frequently debated topic. If the circuit breaker has grading capacitors that you have access to i.e. Live Tank CBs then it is recommended to test these to verify their value. Most manufacturers don’t recommend Power Factor testing SF6 dead tank circuit breakers. To check the quality of the SF6 gas i.e. the insulation of the CB, it is recommended to perform a moisture and purity test on the SF6 gas.
There have been some reports that you can determine some issues within the CB contacts with a Power Factor test, so several utilities still promote and perform these tests on SF6 circuit breakers. If you perform PF testing on your SF6 CBs remember that you will have very small capacitance values and that your primary evaluation should be of the watts lost and the leakage current. A hot collar test may also be performed to evaluate the condition of the porcelain and the external insulation elements.