Canonical URL is the preferred URL search engines should treat as the main version among duplicates or near-duplicates.
It matters because technical issues can prevent great content from being discovered, rendered, indexed, or trusted. Strong technical foundations protect rankings during redesigns, migrations, content expansion, and platform changes.
Example
A product page may identify its clean URL as the preferred version while tracking parameters create other accessible URLs. Keep canonical signals consistent with internal links and redirects, while recognizing that the search engine ultimately selects its canonical.