Knowledge Base Help & Documentation:
What is “Enable SEO-friendly URLs” option?
If you choose this option, after the Migration all internal links (those connecting elements inside the site) on your new website will be built according to the SEO URLs structure you configured on your Target website (the one you’re migrating to).
In case you didn’t make changes to SEO URLs settings on the Target site, the URLs will be formed according to the following structure: yourdomain.com/category title/page title.
If you want to change your SEO URLs structure on the Target website, it is strongly recommended that you do it before the Migration. If you make changes after the Migration, the internal links on your Target website will not work.