In reply to mutt:
in the "it depends" camp, here is some food for thought:
- just because it's stuck, doesn't mean it's actually a bomber placement.
- Cams last a while but the wires on nuts rust away pretty quickly and if you've never found a nut that looked "a bit rusty", try bending it around or bouncing on it and you'll likely find it snaps with little encouragement as the corrosion is much deeper than it looks.
- what if it's a bad piece where you want to place a good piece? What if it's stuck in a crucial jam location?
- What if it's in a dubious or expanding flake? Do you clip it or not?
- If you can't see whether it's any good, do you end up putting your own piece in anyway and the only result is that you spent more time getting pumped trying to evaluate the situ piece?
- Is it aiding if you end up partially pulling on it because that's just how your hand fits in a crack?
- At what point should situ threads be replaced, does it change the grade if you just replaced a bunch of old terrifying, frayed threads with brand new shiny ones?
- If there is a position for a thread, how awkward should the placing be before you can legitimately put in a situ thread? Or can any thread just be left as a situ piece?
- What kinds of situ gear can a well-meaning climber clean out? It's probably fine to fish out old nuts (I once managed to find 5 nuts in the same placement and remove 4 of them while climbing a classic) but should you be removing a thread? Presumably you shouldn't be removing a piton?
..... in short, the answer to your question is an unending good old British Ethics debate