How about these sentences:
5) It is good staying here.
6) It is useless staying here.
7) It is not much use staying here.
Would you say they need a comma?
Hello again, Navi,
No, those sentences are perfectly fine without a comma.
navi posted:I don't know why '1' and '3' seem very bad to me and these three don't seem that bad.
Yes, it's a tough nut to crack, Navi. I think a thesis or dissertation could be devoted to this topic. Hassan Hussein asked about it recently, and I really liked Gustavo's reply, which drew upon and clarified a much older GE thread -- one which occurred before I even knew of the site. Have a look at these two threads:
I think Gustavo has given some good general guidelines. If we think of adjectives as lying along a semantic continuum from subjective/emotional to objective/rational, it is the subjective/emotional adjectives that have the best chance at working in the "it"-extraposition structure with a gerund.
I think the generalization may be a bit shaky in places. For example, I think it sounds equally acceptable to say "It is fun swimming in the river" and "It is dangerous swimming in the river," even though "dangerous" is more objective and rational than "fun," which is clearly subjective and emotional.
(Edit: I suppose I find the sentence with "dangerous" slightly less acceptable.)
What's clever about your question set (your opening gambit and follow-up) is that, in terms of Gustavo's post, it shows that "good" can have objective/rational or subjective/emotional meaning, and that it's only when used with subjective/emotional meaning that this structure has a good chance of working.
I have it easy as a native speaker. All I have to do is not think about it and everything works out fine.