What should you do with old user directories after a failed Apache NetBeans upgrade?

Apache NetBeans keeps per-user configuration in a version-scoped user directory — for example ~/.netbeans/<release> on Linux, with OS-specific equivalents on Windows and macOS — and installing a newer release creates a new directory rather than modifying the previous one. On first start, an import wizard offers to carry settings forward from the most recent prior release. Exact locations vary by operating system and release generation.

The IDE provides no automatic rollback and never deletes user directories left behind by older releases. After an upgrade that does not go as planned, that leaves two unresolved choices: import the previous settings and risk carrying forward a plugin or configuration incompatible with the new release, or decline the import and start with a clean profile, losing templates, keybindings, and user-installed plugins. Meanwhile, old version-scoped directories accumulate on disk with no built-in cleanup.

Which factors should determine whether importing prior settings or starting clean is the safer choice for a given upgrade? Once a new release runs reliably, can the older release's user directory be deleted without affecting the newer one, and what exactly is lost when it is removed?