I just returned from an Intensive with Boon. We used the "Boon Mix" of akadama, lava, and pumice on everything we potted. That's the mix Boon likes, but it's not the only mix that "works". If those materials aren't available to you, use something else that is.
Akadama is a fired volcanic clay from Japan. It will hold a little water to slow release to the roots as they need it. But it also allows roots to have good exposure to oxygen. It promotes rapid root growth. It does bread down over time as the root system grows. So, you have to repot.
Pumice doesn't break down, a help promote good drainage.
Lava is light, and has an open structure, again promoting exposure to oxygen for rapid root growth.
All the above make for a fast draining soil that will help keep your roots from developing root rot from sitting in too wet conditions.
If you live in a hot climate, you may have to water often. Maybe more than once a day. That's the tradeoff. Using a totally inorganic soil requires organic fertilizer and attention to watering. Your reward for that is awesome nebari and excellent health of the tree.
Many commercial operations add organic material to their soil mixes because it is "safer" for them. It will hold more water, so they are less likely to lose material due to lack of water. It's also less expensive. Their tradeoff is the plant is not as healthy AS IT COULD BE. They also tend to use the fertilizer salts. Their purpose is to keep the tree alive until it is sold, not to develop finished bonsai.
There are certainly exceptions to the above paragraph. Just know that one of the first things that needs to be done when you aquire a bonsai, or bonsai material, is to evaluate the soil it is in. If the soil needs to be improved, do so at the earliest appropriate time.