This forum is more searchable and manageable than the Discord, so anything that deserves archiving should end up here. In particular, any bug reports and feature requests must be published here (#bug-reports and #feature-requests) to be tracked. You can also post help questions in #help. There’s also a #knowledge-management category for all kinds of useful discussions, and a #share-showcase category for sharing or showing off anything related to Obsidian.
Naturally, searching the forum before asking a question, reporting a bug, or asking for a feature is crucial as someone has likely thought about the same issue before.
The Discord chat is a faster-paced, more casual environment. Many things are discussed there first before being published here. Feel free to discuss anything the channels there facilitate.