The new consumer unit not only brings the dwelling up to the standard that is required by the latest Government rules and regulations but it also allows the owner to consider the present distribution of the electrical power circuits. It may well be that there requires to be a change in how the power is distributed and the circuits protected after a re-evaluation of the present circuits.
It was quite common in the past to double up circuits on one fuse or put all the lights on one circuit. Nowadays circuits are broken up into more distinct units so that if there is a fault on any circuit it only takes out a small part of the total power usage and leaves the bulk of the circuits running as normal. Obviously a lot of the circuits were wired years ago and cannot be refined at a later date without a good deal of rewiring but if certain changes can be made simply and without too much disturbance then it is worthwhile considering the options.
Splitting lighting circuits in two is a major change that is really worthwhile and dividing some of the socket circuits can help. Total loss of light and power can be a real pain and if it can be avoided then it should. A good electrician will provide advice as too what is possible and the cost entailed in doing it. It should be possible to make changes without too much disturbance and redecoration, but in some cases it may be well worth wire considering rewiring the building to get the circuits up to modern standards
The installation of a new consumer unit allows new circuits to be considered as the new box can be bought that will allow extra outlets, it also allows consideration as too how those circuits will be protected, whether by RCD alone or whether to include overcurrent protection as well in the form of an RC O. In some cases there may need to be an exclusion outlet or the more usual individual outlet to accommodate a fire alarm or a burglar alarm. An individual outlet will mean that this circuit will not be power restricted unless this individual line is damaged and the usage of protected or armoured cable will keep the circuit going when most other circuits fail. A final item is to choose what sort of box is required it may be surfaced mounted or can even be a flush mounted unit.