I was not referring here about the "activity" per se, I was talking about quotas and percentages of use. No matter for what kind of activity you are going to use the service, I would like to have clear from the beginning what limits of use I have.

Another thing completely different is the permissibility about certain illegal activities or loopholes in their servers. That's not my concern, that's only a question of moral/ethics/legal between the client, the provider and the authorities.