It depends a lot, if he doesn't need to have a customized configuration for each site, I don't see a problem in configuring the APs in a single network (think of a site that concentrates all services).
I particularly like to have separate networks and create templates for easier management. But I don't think I have a general recommendation.
And yes, I would have to reconfigure everything again.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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