At my employer we have an emergency location (glorified office) that we basically never operate out of except one afternoon a quarter to prove we can. The documentation about how to operate out of that site includes a warning to that effect.
Edit: Now that I think about it building has been remodeled so I should really have someone confirm if the warning is still valid.
Contractually required. Clients want assurance of continuity of business in case a meteor hits our office or an errant backhoe hits the fiber on our street. We use it for real about one day every 2-2.5yr. It's only enough space for the dozen key people we need to field urgent stuff.
Previously we had clients required us cross train a handful of key employees on their specific stuff so they could acqui-hire those people to maintain their stuff in the event our company went tits up on short notice (we actually saw them exercise that with a prior vendor). They no longer do that as we're much bigger now.
Finance stuff. Where I work it's more of an inherited checkbox than an actual mission critical requirement but I suppose it would help us if it really came down to it and the customers see enough value in it that they pay for it so...
It makes sense to have a business continuity plan for various scenarios that could render the primary office location unusable (power outage, natural disaster, police closing the area for some reason, ...).
For many businesses, WFH or "everyone goes to the Winchester, we have a nice cold pint, and wait for all of this to blow over" could be valid options, but if you want to have business continuity, having at least a small office where the disaster recovery team can meet and coordinate things from makes sense.
A contract for guaranteed priority access with a coworking space would likely be the easiest option unless you need some custom infrastructure though.
Edit: Now that I think about it building has been remodeled so I should really have someone confirm if the warning is still valid.