A Resource Group (RG) can have individual resources under it that could belong to any of the Azure regions. So then, is there any logical meaning for 'region' for Resource Group? Does it really dictate anything? Or maybe it's just more like satisfying a unified model of Azure that pretty much everything should belong to some region, even if in minority of the cases it may make no logical sense?
A resource group is like a container that holds related resources for an Azure solution and you manage them as a group. A resource group can contain resources that are located in different regions.
"Why does a resource group need a location?" The document gives a detailed explanation.
"If the resources can have different locations than the resource group, why does the resource group location matter at all?" The resource group stores metadata about the resources. Therefore, when you specify a location for the resource group, you're specifying where that metadata is stored. For compliance reasons, you may need to ensure that your data is stored in a particular region.
If the resource group's region is temporarily unavailable, you can't update resources in the resource group because the metadata is unavailable. The resources in other regions will still function as expected, but you can't update them. To minimize risk, locate your resource group and resources in the same region.