Even for TDMA networks you need some surprisingly precise idea of where the user is (more precise than which is used for call routing) for the radio interface to actually work. This has to do with the need to compensate for speed of light to retain synchronisation of the radio interface framing (for GSM-like TDMA this is mostly relevant for rural areas and gets you precision of ~250m, but it has to be significantly more precise for CDMA) and with planing of handovers.
Storing some of this stuff might be valid for diagnostics and network planning, but it is mostly stored as part of government required (meta)data retention policies. Whether telcos really have to store this kind of data is somewhat questionable and certainly jurisdiction-specific, but usually they just dump all signalisation traffic somewhere and are done with it with the expectation that it is simpler and cheaper to store all of it than to design (which involves legal analysis) and implement some kind of filtering mechanism.
Storing some of this stuff might be valid for diagnostics and network planning, but it is mostly stored as part of government required (meta)data retention policies. Whether telcos really have to store this kind of data is somewhat questionable and certainly jurisdiction-specific, but usually they just dump all signalisation traffic somewhere and are done with it with the expectation that it is simpler and cheaper to store all of it than to design (which involves legal analysis) and implement some kind of filtering mechanism.