Putting questions "on hold" or the closing of questions is a recurring phenomena seen on this the Chemistry StackExchange site. Most questions I have seen so far have been closed for good reasons, such as being a repeat or lacking evidence of research on the part of the question asker. However, I feel that there are some issues about putting questions "on hold". One of the main reasons why questions are put "on hold" based on my experience is that the question is "unclear". Which is extremely uninformative to the question asker.
Indeed, an "unclear" question may demonstrate a lack of communication skills of the question asker. However, it also a lack of communication skills on the part of the moderator. The reason being that the moderator does not know how to communicate why the question is "unclear" or how the question is "unclear". This sort of labeling of questions as "unclear" is evidently not beneficial to all parties, the moderators, the question askers and the rest of the community of users. In fact, such a label is equivalent to a baseless accusation because it is not substantiated by any evidence at all.
Hence, may I suggest that in addition to labeling a question as "unclear", moderators also provide sufficient reason to support their claim? For example, they could make reference to parts of the question (i.e. particular phrases or sentences) or clarify the meaning of particular words which are ambiguous.
This is different from downvoting because putting a question "on hold" is more of an official course of action taken by the "all-powerful" moderators. Thus, it is also more serious, in my opinion.
I hope actions aimed at improving this situation would be taken as this labeling of questions severely compromises user experience on the site.