I'm still new to it, so I'll have more to say in a few years! But basically biochar holds water and nutrients so it's an excellent soil amendment.
We use the word "biochar" pretty loosely. Technically, what you're making in the retorts is simply charcoal, and you inoculate the charcoal with compost tea, leaf mold, urine, etc for several weeks to make biochar before adding it to the soil.
My goal is to fold the charcoal directly into our waste streams (into the chicken deep bedding, into the compost bin) so that our compost already has the charcoal as part of it.
If you want a fun video on the inoculation process (which also gives some background on biochar)-