If you just want to cut an odd service here and there on already highly served routes, that'll do a lot less harm than leaving rural communities stranded. Especially if you cut an odd off peak/early morning/late evening service
However, as a general rule of thumb, the NR costs are fixed and the extra infrastructure costs of running a train is generally covered by the track access of said train.
Therefore, whilst cutting a train from a busy line would be broadly cost neutral if the income broadly equals the TOC costs, of the train is busy enough to make more than a small profit then cutting it could actually cost the industry money and therefore increase the subsidies required from the government.
Arguably, the thing to do is to find sections of lines which are generally lightly used but could cater for a lot of people (for example they could run metro services or provide new station pairings between stations otherwise hard to get between).
One which could cover both is too run a service from Basingstoke to Farnborough Main (on the slows, where there's 3tph for passengers and intermittent freight, but unlikely to be as many as 3tph, so an extra 2tph on top of that is still an average headway of seven and a half minutes, so hardly stretching capacity) before using a new grade separated junction to connect to Frimley and then onto Ascot (increasing the line from 2tph to 4tph, so again hardly busy for a line with tracks in both directions).
That connects Basingstoke with more of the Aldershot Urban Area (Frimley and Camberley) which is currently hard to get to by train (yes there's buses, however by needing to change even for those who would see using a bus as acceptable it does their journey down) and increases the frequency between all stations and the Aldershot Urban Area (with a population of around 250,000 people it's on a par with Milton Keynes and Plymouth).
I've also previously suggested a similar setup for Manchester with a service between Clitheroe and Chester (with a new junction so the trains go direct from Salford Crescent to Eccles and missing out central Manchester). Whilst that would miss central Manchester, it would mean that for several stations they could see their frequency change from 1tph to 2tph and whilst the second service might involve a change, it's still going to be far more useful than the current service.
Also, by improving rail capacity it could even increase the economy of the area and therefore even if it doesn't change the cost of the railways it may reduce the percentage of the cost of the railways of the government budget:
Baseline
1,000 economic value of the UK
400 total government spending
6 government support to the railways
Make changes to the railways like suggested (focusing on covering TOC costs of new services without significant new infrastructure):
1,200 economic value of the UK
480 total government spend (increases proportional to the above)
6 government support to the railways.
Whilst the total level of support to the railways hasn't changed its become a smaller percentage.