I flagged a post and (choose one)
- my flag was marked as helpful, yet nothing was done
- my flag was marked as declined, yet the post was deleted/edited/closed
Case 1: your flag was helpful, but nothing happened. Causes include:
Case 2: Your flag was declined, but exactly what you wanted to happen happened (e.g. the post was deleted). Causes include:
Alternate explanation that applies to either case: a moderator clicked the wrong button by mistake and it's not a big deal. For genuinely bad posts, other people flag them too, so they end up solved.
Flags are marked helpful when the moderator judges them to have merit, and declined when the moderator judges them to lack merit. Flags have merit when:
The flag is being used correctly; it is highlighting a problem that may require moderator action, and not something best handled by the community, like evaluating the technical correctness of a question, and
The moderator understands why the flag is being cast. Counter-example: Not an Answer flags on answers that are clearly attempting to answer the question, even if the answer is misguided.
Flags are declined when these two conditions are not fulfilled.
But the moderator still has to decide whether or not to take action on the flagged post. "Declined" and "No Action Taken" are not the same thing, and moderators might actually take some action on the post anyway, irrespective of the flag that was cast.
One common reason that a flag may be marked helpful but no moderator action is taken is when the user corrects the problem with their post after a moderator flag has been cast on it, but before a moderator has seen the flag.