ZE: What are `defaults` used for?

[zFernand0]

Is your request for enhancement related to a problem? Please describe.

It's hard to know what defaults are used for in the context of Zowe Explorer for VSCode (and likely the same applies to its IntelliJ counterpart)

Describe the solution you'd like

We should better describe how and why default profiles are used in Zowe Explorer (VScode) 🙏

Related doc pages

https://docs.zowe.org/stable/user-guide/ze-managing-profiles

Additional context

This came form a discussion in Zowe Explorer:

• zowe.config.json: what is "defaults" for? zowe-explorer-vscode#3426