Trying to get the most out of waste streams. Most food is produced as energy goes up the food chain, this is making use of the otherside, the decomposition phase.
I share te hobby with 2 other guys I work with, we have each bought mycellium once or twice and share it out, from there we just keep expanding it. Try and keep a little in a bottle in the fridge in case we get some infection which happens a bit. Ocassionally buy a new type or strain, just to experiment, but it is not necessary. Best trick I find is when a batch is almost spent, just mix it in to new substrate and it starts all over again, ever expanding.