sleslie99 think of each widget (regardless of html, handlebars, or react) as its own black box. The widget can then be placed onto a page template. If you add a widget to the header / footer template, it will appear on every page like a global announcement. If you place the widget on a forum board template, that widget will appear on every forum board page across the app. If you place the widget on a page template for a specific set of forum boards only, then the widget should only appear only when viewing those specific forum boards.
HTML widgets are meant for non developers to easily use the editor to get some rich text message out there quickly. They do not support any dynamic logic or coding.
Handlebars and react components do support logic, configuration variables, and coding. This means a single widget could have multiple options or permutations that load dynamically based on the configuration variables an admin can set when adding / configuring the widget or based on other properties like the node id or the user. This means you could create one widget and add it to all forum board pages but the logic in the widget could determine to show only for specific users, on speicific boards, only when the forum board is public vs private or any other custom field / variable you’d want to specify as part of the configuration of the widget.
