It is common in English to use it as a preparatory subject when an infinitive is the subject of a sentence.
It is necessary to wear a tie.
I also understand this rule is comparatively uncommon in a gerund.
Then, how about the following examples?
Do they sound very awkward?
I would like to know the degree of the unacceptability of the expressions.
(A) It is necessay wearing a tie.
(B) It is necessary being registered on this forum.
In (B), I intentionally took the form of a passive gerund (being registered) as I think it would be possible that (A) is acceptable but (B) is not.
If my wild guess correct, it might be not because of the usage of gerund with preparatory "it" but the passive gerund (being regiestered), which seems to sounds too formal or unnatural to the natives.
I will thank you for your good advice.