I suppose the big benefit of it is it makes long distance connections quite a lot easier. I was able to travel from Oxford to Nottingham and back in a day (with several hours in Nottingham) for about £23 (15 for bus + 8 for train), but that was only possible because of the X5 and X7 - even just splitting the X7 makes the whole thing harder. I suppose they design routes for normal customers and not people trying to travel halfway across the country on the cheap, but I do appreciate the connections. Unless we moved to a Swiss-style system where everything connected perfectly, through routes will always be appreciated (though I appreciate the difficulties it presents for logistics and timetables).
A couple of other examples - the North East has a few. The 19 from North Shields to Northumberland Park is a fairly normal length, but half of the journeys extend to Ashington, completely out on a limb from the rest of their network. There is also the 26 - seemingly formed from taking the already long 27 (Newcastle to South Shields), and then looping it around several other estates. Not only is the Metro far faster, but it is also faster to wait for the 27 which leaves around 10 minutes after the 26. Even getting the Stagecoach X34 is faster - and that only goes to the peripheral estates of South Shields, but even factoring in the extra bus to get to town, it's still faster. Yet of the three (26/27, Stagecoach day ticket, Metro), the 26 and 27 are the most expensive...