Ensure you have enough space before upgrading to Big Sur (UPDATE)
UPDATE: The revised macOS Big Sur 11.2.1 released on February 15, 2021 checks to make sure there is enough available storage before the installation begins. If you have questions regarding an upgrade to Big Sur, please contact CCIT Support.
Previous story from February 12 follows:
If you plan on upgrading your Mac to the newest operating system, macOS Big Sur (11.2), please ensure you have sufficient free space on your hard drive before beginning the upgrade process. If upgrading from macOS Sierra or later, macOS Big Sur requires 35.5GB of available storage to upgrade. If upgrading from an earlier release, macOS Big Sur requires up to 44.5GB of available storage.
You may encounter irreversible data loss if you upgrade to Big Sur from a previous operating system without sufficient space. You can check your free space by selecting Apple > About This Mac > Storage.