Modern attitude to herbal usage may account for some of the confusion over their suitability. Stores are filling up with powders, pills, tinctures, teas & chunks of herbs; labels tease with sellers hints of benefits.
Traditionally herbs were the province of a select individual. This is only partly due to the fact that technical literacy has not always been common. Power to produce "cures" was not given away readily.
In many instances there was/is the societies' healer; and in clans an elder who were/are practitioners of their herbal craft. Those situations indicate that an apprenticeship was/is the original way to gain experience.
A significant part of learning just what to do was learning what to use. This includes the obvious aspects, such as exactly when to harvest curative plants, precisely which parts to use in different instances & how to process them.
Herbal processing may be more important than western students think. A scientific inclination to look for an active ingredient, to parallel drug pharmacological action, is what drives current scientific herbal research. In other words the herb must be put to test.
Yet when an herb is tested, it may have been with plant tissue that does not really correspond to what an indigenous herbalist would use. The most accessible non-western herbal pharmacology might be from China, where centuries of written herbal records exist.
Some Chinese medicinal plants collected have their unique technique for processing, they are not all just dried for storage until infused or powdered. Ingredient lists are common, but the traditional way to process them is rarely considered.
Internet searches/books can tell us what, markets are ready to give us where, yet we may not always be doing things how.