Video summary: link

An Organization is mainly used for billing purposes to centralize billing of all your different workspaces. Everything related to your billing is in your organization settings.

A workspace is the environment where you're working.

Usually, sales teams and solopreneurs only have 1 organization and 1 workspace (because otherwise it's overkill and more will kill your productivity, you better use different lists and pipelines to separate different activities).

On the other hand, agencies will tend to have 1 or multiple organizations and multiple workspaces.