E.g. because the chat assistant is able to…
- search your database
- search the web, Wikipedia or PubMed on its own, even when using local models like Gemma 3
- download links (e.g. of web pages or even item links) to retrieve additional information
- optionally change properties (e.g. tags) and contents
- process annotations of PDF, RTF(D) and Markdown documents, e.g. summarize them
- return item links (e.g. links to sections/pages in Markdown, EPUB or PDF documents), e.g. in a summary or table depending on your prompt
- use multiple models from various providers in one chat
- handle also third-party document formats that were indexed using Spotlight’s plug-ins
In addition, contrary to uploading documents in the chat app of your choice, DEVONthink performs various steps to increase the security & privacy. See DT4 - privacy when using AI - #6 by cgrunenberg
And of course it’s much more convenient than switching apps and uploading documents 
What’s your time zone?