Daniel P. B. Smith wrote:
Once a "citation needed" tag is in place, there's no need to do anything in a hurry. The reader is adequately warned, other editors are informed.
In many many cases, this is true. But not in all.
The one that is absolutely imperative for all editors is to recognize that "If this claim would be libellous if false, it is absolutely not acceptable to simply put a 'citation needed' tag and hope for the best."
It is extremely painful to see those. "Lord John Doe was a porn star in 1943. <citation needed>" In such cases, being a citation nazi is the right thing to do.
That is not the only case, but that is the one where it is absolutely imperative.