This article shares some possible use cases you could support, as well as an example flow that supports each use case. You're certainly not limited to these use cases, but they can be a helpful jumping off point as you plan your implementation.
You can manage custom embeds on a site, including updating the embeds' positions after a site structure update.
This flow demonstrates how to list existing embeds, update their content and position, and create new embeds.
You can add a banner to a Wix site with a custom embed.
To add a banner to a site: