Pot in a pot in a pot concept.
30 odd years ago, don't know exactly when, some seedlings Santa Barbara Orchid Estates was growing, got out of hand and were growing into each others pots etc. Paul Gripp instructed his help to up-pot them. There were so many seedlings and not enough help that he took a shortcut and told the guys to just place the 2 1/2" pot seedlings into a larger pot without the bark and the redo in order to save time. This would at least separate them from each other and they would come back in a month or 2 to do it right.
The month went by and when they came back a year later he found that the plants were doing just fine without their help, thank you very much.. Roots were filling the empty space and the plats were developing fine. The light went on for Paul and he decided to leave them like that and just move them up into a larger pot when necessary. At least for the West Coast, the pot in a pot idea originated there and SBOE has used the concept extensively ever since.
I got the idea from them in 2,000 and have used it frequently for my potted plants. You take a small plant in a small pot growing in whatever, bark, rock, cocconut etc and when it needs a larger pot place it into a larger EMPTY pot. The roots will circle along the walls and eventually fill the empty space. When the plant grows over the edge of that pot, repeat the process with a slightly larger pot. Eventually you'll end up with a large plant growing in a honeycomb web of multiple pots without any growing media. The original media, even if it is 5 year old bark, never needs to be changed as it makes up such a small percentage of the total growing volume and can be safely ignored. It will deteriorate and wash away in time.
Never needs to be repotted, cannot be over watered and in my opinion is one of the best ways to grow potted plants. The photo shows a small Cattleya overgrowing it's seedling pot and now growing in a 4" square. I add large, 1 1/2" to 2" rock to add stability so it won't tip over. The rocks do not contribute to the growing needs of the plant. Eventually the roots will bind everything together.