They cause a major disruption to the existing SERPs pushing many different universal SERP features down the page.
Featured snippets, Local packs, People Also Ask, Find Results On, Shopping, Ads are all likely to be redesigned or disappear completely.
Results will vary by keyword query and intent. Some AIO results will be prepopulated for certain types of queries whilst others will only feature a simple AIO ‘Show More’ link.
There are huge risks to your existing organic positions and traffic, e.g. You could lose a Featured Snippet and be replaced with just one of many citation links.
There are also huge opportunities (especially for sites ranking outside the top results) to get referenced in generative AI search
These changes will impact how you update, create and publish content to rank well in future