In Spain, especially after the closures in the 80s [1], the traditional rail network, which was already chronically under-maintained, also became, with some exceptions, hopelessly disjointed. Many of the remaining operating routes can't meaningfully connect the territories they pass through with each other, only to Madrid.
As more and more of the main cities are brought into the high speed network, the traditional network is given less funding and less service, to the detriment of the smaller towns served by it. However, it is important to note that this trend was already underway before the high speed network was in place.
The remaining regional train between Barcelona and Madrid, for example, takes eight hours by the schedule (nine or ten in real life) while the high speed trains take three hours or less.
Occasionally, some services survive that use the high speed network for most of the trip, then switch to the traditional network for the last leg of the trip.
I'd expect them to have cheaper tickets between the same cities, if you don't care about the speed.