The relevance of aspect for the correct usage of verbs seems to be explained only for the personal moods of verbs (e.g. indicative), but what is the meaning of aspect for the impersonal moods, such as the infinitive or the imperative?
To clarify, whereas I can detect a certain difference between Я открываю окно and Я открою окно, I don't understand how one would choose between the two aspects in the imperative. Is there a difference between Открывай! and Открой! ?
I once asked a native speaker about this, and while they acknowledged the two forms to have roughly the same meaning in the imperative, they seemed to think the imperfective implied more urgency of the request. As an example, a person requesting access multiple times would say:
— Открой! (pause) Открой! (pause) Ну открывай же!
But somehow this doesn't quite fit in with my understanding of aspect. Similarly, for the infinitive, what is the difference between Нельзя открыть окно and Нельзя открывать окно?