At least that's a somewhat constructive objective.... imagine having a vault that's nearly capped out on resources and you get make 16 couples dance, and when you do so, and forget time they create babies... so now you have 8 pregnant dwellers and the systems tells you to go deliver 16 babies. Fair enough, all personnel to the porm-pad again... and THEN you get the objective to have 12 dwellers pregnant..... yep... in that order
Or, also a great one, rush [x] times succesfully, or have a lot of fires/incidents successfully managed. Basically this is a moneyburner for me because if the vault is rather large, I tend to just make an elevator out, tiny cheapest 1-space room like a diner, and chuck 2 reasonably high dwellers in there with good guns. Then keep rushing and don't care about 10% happiness...
Same for merge/upgrade [x] rooms. Make a diner, add diner. Destroy. Repeat.
Or make a diner, upgrade and then destroy
Time consuming and annoying. Still not as bad as deathclaws though, which IMO need a bit of a tranquilizer shot. To the face. With an ICBM. I'm afraid to send dwellers out to the wastes now... every 2nd guy I send gets me those critters...
EDIT
I think I found the difference between unique dwellers or any dwellers in objectives...
May need further testing, but I think if it's written like "Dwellers" (with a capital D) it's unique ones, if it's written as "dwellers" (without the capital) it's any.
EDIT 2
It seems to be the other way around.... can't say for sure because not many rooms/objectives like this...
Can anybody help verify?