IP, analog or hybrid - and why factories often stay hybrid
A pure IP PBX runs every extension over your data network. Handsets are IP phones or softphones on a PC or mobile, and adding an extension is a configuration change rather than a cable pull. For an office building with structured cabling already in place, it is clearly the right architecture.
A factory is often a different case. Extensions may need to reach a gate hut, a weighbridge, a store two hundred metres away or a shop floor position where there is no data network and no realistic prospect of one. Analog extensions run happily over simple two-wire cable across those distances, tolerate industrial conditions, and keep working when the network switch does not.
Hybrid systems support both, which is why most industrial installations in this belt end up hybrid. Offices get IP handsets with the features that come with them; remote and harsh locations get analog extensions on existing or easily-run cable. One system, one dial plan, no artificial split.
The other practical factor is what your incoming lines look like. Many sites still have analog trunk lines alongside SIP trunks from an internet provider, and a hybrid system terminates both without forcing an all-at-once migration.