I am just quoting a passage from an article on potency by J T Kent in his lesser writings:
"There is a wonderful latitude between the tinctures and the C Ms and in my judgment the selection of the best potency is a matter of experience and observation, ranging from the tinctures to the highest potencies, with the possibility of bringing out some useful rules for the guidance of others. The various potencies are all more or less related to individuals and it is the individual that we should study. We might well begin with Hanhnemann's statement that the 30 is low enough or strong enough to begin with. For many years I have found it strong enough to begin with. Individualization. in regard to potencies as in other branches of homeopathic work, furnishes us with an additional element of accuracy and success, enabling us to reach certain cases that we otherwise could not reach. Some patients are cured mildly and permanently by the use of 200th or 1000th. There are other individuals who are torn to pieces by the use of the highest potencies. The indiscriminate use of any one potency is very likely to bring reproach upon our art. They all, from the 30th to the millionth, have their place, but no single potency is equal to the demands made upon it by the diseases of different individuals. Then the nature of the disease makes a difference: patients who have heart disease, or who are suffering from phthisis are apt to have their sufferings increased and the end hastened by the highest potencies: they do better under the 30th or 200th. Some times very sensitive patients will do well on a high potency if they have been prepared for it by the use of a lower one."