We fly the aircraft as necessary irrespective of whether the seat belt signs are on or off.
In Boeings there is a bank angle selector you can use to force the AP into only conducting turns up to and including that angle. Most times it’s set to auto.
Normal operations you will bank to a maximum of 30 degrees. Any more than this (>35) and the primary flight computers will introduce a progressively heavier feedback through the column. Above 35 degrees you will also get a bank angle audio warning.
The Boeing will ‘advise’ you that you are exceeding the bank limits but will let you, the Airbus will just limit the bank.
The seat belts are put on in cruise if we encounter or think we are about to encounter turbulence. It means the passengers get strapped in, no toilets and no hot drinks to be served. That’s all.