This pattern expresses that the second action or state occurs immediately after the first, often with a sense of suddenness or inevitability. It is a written, formal construction, frequently found in literary works, news reports, or narrative prose. In conversation, you'll rarely hear it; people would use ～たとたん or ～しだい instead.

The nuance is that the second event follows without any pause, and often the first event triggers the second. For example, 家に帰るなり、叫び出した means 'the moment I got home, I started screaming.' Because it's formal, it can sound dramatic or literary.

Be careful with the placement: it attaches directly to the verb's dictionary form, but not to the ます-stem or て-form. Also, note that the subject of the two clauses can be the same or different, but the pattern emphasizes the quick succession.