At any given time I’ve got an open soil mixing tub (or more than one) for use in potting up new plants. It’s got whatever I’m using for my current soil mix in it, and that’s where I keep handy any amendments I may have on hand to mix in, or garage-sale bags of commercial potting soil. I bring all my old spent pots and containers back to this location and add them in as well, throwing out any
roots and stems that are too large in the process. (They go in the bottom of larger pots later.) I often have an anaerobic pot that I put in
water in a failed effort at revival and then forgot about; it goes in the mix with no harm.
I guess what I’m saying is, it’s fine, but the way I would use it is to mix it with other soil; I wouldn’t plant back into it unmixed.