So one of the main things we do is automatically sync-ing documents from different sources of knowledge from your team. So all of the data connectors as well as the user authentication and access systems would have to be built from scratch if you did your own. Also if you have more than a few documents you would have to recreate the RAG pipeline (and ours is fairly involved so it would be quite some work). Finally there's the UI and other features like learning from feedback, usage analytics, chat history, etc etc.

If you're just looking to upload a few personal docs into a chat assistant for your own use, probably Danswer is overkill and more complex than the effort is worth. If you're thinking of a team wide use case, then using Danswer makes sense.