Again, research "meeting of the minds". It's a standard legal term directly relevant to all contracts and terms. Also, "transparency" is another important one.

Many online services have very wide terms around what they can do with your data, which most people who bother to read them interpret as being what is required for them to handle the service for you without breaking copyright law. In that context, being able to use and analyse your data to improve their services could be another catch-all that lets them do specific performance optimisation on their backend.

One party instead deciding they've got blanket permission to do whatever they like with your work, including selling it to others, may well not hold up in court.

Contracts aren't programs and one party tricking the other rarely works out in court - courts world-wide tend to rule against trickery and deception.