RCD protection for sockets is required when they can reasonably be expected to be used with equipment outside the house, for example garden tools. This is especially likely with downstairs sockets. You are not required to protect sockets that will only be used for indoor equipment.
You could not reasonably expect that someone will plug a long extension lead in at the loft to operate a lawn mower, when there are numerous other sockets readily available in the house.
It is generally considered wise, but not currently a requirement, to RCD-protect circuits that are used with water in the bathroom, for example electric showers.
It is widely considered inadvisable to put fixed cookers and immersion heaters on an RCD, because they are prone to earth leakage and nuisance trips. They are OK on RCBOs because a trip will not cause a nuisance on any other circuit. Provided the cooker switch does not incorporate a socket
as there is little chance of the cooker itself being carried outdoors and used.
Although it is not currently a requiremnt, many people prefer to see kitchen and utility rooms protected by an RCD, even if they will not be used with equipment outdoors, because of the presence of water and appliances such as kettles and washing machines.
edited: This was a response to mdbalson, not arguing with securespark