Just address the ‘are narrow band‘ elephant. All RT sets, regardless of mode and status, are ‘narrow band‘ modulation with a variety of narrow frequency spacings.
So the very narrow NB modes (sometimes analog but mostly digital data or DV use) and spacings, such as Digital mode on PMR446 and in aviation implemented on some equipment and spacings appropriately, is used on operational modes that use that facility and it’s often auto set to that mode when needed on modern kit with that facility.
So there’s two distinctively different uses of NB when it comes to modes and frequency use/spacing. And don’t forget, mostly applicable to GenCon receivers and ham gear, additional NB filters which are used to improve selectivity and aid cleaner discrimination of weak signals in congestion of frequencies and poor propagation and interference conditions.
But as pointed out in a previous post, some instances the spacing and modes exist for other licensed operation usage or subdivided other licensed use within a broader licensed allocation use or simply because it was an inherent requirement on that radio for conformity of similar or interoperability.
It doesn’t necessarily mean it’s presence makes it necessary or even within license use on your licensed use. But that’s very license and region specific.