What is the "location" header for in Journal entries?
Whatever you want to use it for, CK. I suspect most people put things like "Front Flower Bed" or "Large Blue Bowl" - I use mine for the botanical family the plant belongs to, sometimes followed by numbers, if I want to get really specific, because it gives me a shortcut way to group related plants within my larger categories; and I usually try to grow related plants near to each other. When you have a LOT of plants, sometimes you can't remember what you have done with them and then you can find a reminder of where you put them just the thing you need to have.
Give it a bit of thought, though. If you move your plants around a lot, you might not want to get too specific, because when you move them around, you will then have to go back and change your entries to match the new locations.