I'm glad that TOCs are still making the effort to produce maps like this, rather than simply pushing everyone into using online journey planners.
Those planners are okay if you need to go from point A to point B. But if I'm staying at point A, and want a day out by train, I might look at going via B to C, then back via D and E. Maps like this show which options are easiest, in terms of connections, without having to look up numerous journeys or timetables.
As one who's unfamiliar with Northern's services, it also makes it much easier for me to understand their structure. My main suggestion for improvement would be to name the operators of the other services alongside the line on the map. But overall it's a useful guide I think.