I’m struggling to understand the following sentence:
You may not collect user or device data without prior user consent, and then only to provide a service or function that is directly relevant to the use of the Application.
What exactly does it mean?
Does it mean:
You may not collect data without user consent. If the user agrees to allow you to collect data, you can only collect data to provide a service or function that is directly relevant to the use of the Application.
Why can the phrase “and then only” be used in such a way?
Your explanation is exactly correct. I couldn’t have said it better myself.
“And then only” says, “Is the first condition met?” In this case, the first condition is that the user consents to releasing information. Yes? We have that consent? Then and only then we have to ask ourselves another question. “Will the information help to fix a problem that the user is having?” Only if the answer to BOTH questions is yes, may we extract the information. If the user denies consent (“No, I will NOT tell you what operating system I use”) -or- If no answer the user gives will help us solve the problem, then WE CAN’T ASK!
That language very typical of the language you will see in employee manuals and such originally written in English.