I can't see a situation where our 50 adding a star on a th10 is ever bad. That was one of maybe two stars on the board he could add. Nothing stopped you from shooting for 2
Because it creates a better environment for our cleaning up to get the 1st star on the TH10 at the same time as we've got a shot at the 2nd star.
Let's say I have a 40% chance at 2 stars, a 40% chance at 1 star, and a 20% chance of botching it. If the TH10 has no stars, then my EV is 1.2 stars added.
If he already has a star, then my EV for attacking the TH 10 becomes a 40% chance of adding 1 star (his second), or 0.4 stars. At that point I'm probably better off attacking a 1-starred TH9 than I am attacking a 1-starred TH10. And there are other people with attacks left who can probably pick up the 1 star on the TH9 I'll get, but they aren't expressing confidence in getting a 2nd star from the TH10.
In other words, unless every other TH9 gets cleaned up, by having gotten 1 star on that TH 10 base we've probably removed any real possibility that trying for the 2nd star is in our best moves.
Or put another way, the chances I get 2 from the TH10 and Jordan can pick up a lone star off a TH9 getting a dragon to the TH are probably greater than the chances that Jordan gets 1 off a TH10 and I am able to convert a 1-star into a 3-star. At least against that opponent with strong walled TH9s.
I think if everyone says, "No, none of us has a good shot at 2 stars from that particular TH10" is the time having lower guys see what it would take to get 1 is the right move.