There's a question today Passenger Lists to USA 1923-1925 that is a simple look-up on Ancestry, which the questioner presumbably doesn't have access to. Takes a few seconds to find the mother and daughter at least.
How should these be answered? Maybe "It's on Ancestry, go look there". (written more politely)? It may appear mean to the questioner that I have the information but won't share it, yet to answer with the details found on a subscription site would violate the terms and conditions of the site.
There's nothing in the FAQ which addresses this, so it's a reasonable question for the OP to ask.
In this case, it's not an explicit request to look up a particular source, but that can happen if the answers start containing the details asked for.
There have been hot discussions on this subject on UK genealogy forums for years, with most forums banning lookups as they don't want to be party to possible copyright infringements.
But I've taken another look and they've become more relaxed about it recently, allowing lookups that don't have any copy-and-paste element (in other words, your own transcript, and no image).
Some UK sites are still specific: "If you persistently offer lookups to other people and provide them with newspaper archive, or use a personal subscription for professional purposes, we also reserve the right to stop your access and to terminate our agreement with you."
So I'm modifying my view on this. If somebody wants to break the terms and conditions of the sites they use by doing lookups, probably we shouldn't stop them, as there's no proof (yet) anything will ever happen as a result.