What are the benefits of this from a passenger's point of view?
If things go 'tits up' with all this rationalisation does that mean that even greater disruption may occur?
Benefits to passengers lower staffing head count therefore a reduction in overhead costs, better traffic management that is signalling in one location therefore route control should be more effective. When a timetable change is made the reprogramming of the system commuters is less onerous likewise for any system config or updating.
Dis-benefits yes there is the risk of a "global" failure this could take out large area, power supply wise there are a number of secure supplies to a site like Didcot at least 1 generator possibly 2, if there is not a second onsite there will be a socket for a second; there will be all manor of UPS's all this will be split into different fire separated rooms likewise the signalling computers and telecoms will be in separate rooms.
There is always some weak links the designers and operators would have risk assessed these.
It should be born in mind that right from the early days of railways effort has been made to reduce the number of signal boxes, the early 1960's saw the introduction of Old Oak Common, Slough, Reading these closed many many signal boxes
