Some have complained that the 4-daily SWT Waterloo-Bristol trains are unnecessary.
*ducks to avoid incoming fire from enraged Bath commuters*
I never said I agreed with them!
To answer the OP's original question, I dont think there are that many truly "unnecessary" routes around these days. Strange, idiosyncratic routes operated twice a day dont tend to jibe well with clockface timetables so most have been removed over the last decade or so. Without wishing to re-ignite the FGW to Brighton debate, this is one of the few good examples of such a service that I can think of in the south of England.
Ivo, you also ask
"Is there really any point in having so many different lines in the Blackwater Valley area?". My answer would be "yes". A number of friends live in this area and benefit from direct or one-change services to London, various parts of Surrey and the south-western London suburbs, Reading and Guildford, and parts of north Hampshire. As a result of having a pretty decent level of rail provision on various routes within the local area, they travel quite a lot by train to see friends, go to events, go shopping, etc, despite being from a pretty pro-car background.
The network in that area caters for various local journeys, of the kind that a lot of people living in suburbia make almost as regularly as the commute to London/ other regional centre.
Most settlements have just one station and one railway line, generally with services to one or two destinations predominating. This set-up, to my mind, offers fewer journey opportunities of the kind mentioned, and whilst it may be set up to cater for commuting patterns, does not offer a good alternative to the car for these non-commuting journeys.