Will uninstalling ArcGIS Pro delete my existing projects or data?

Answer

When users are asked to perform a clean uninstall/reinstall of ArcGIS Desktop, they often have questions about the potential impact on existing projects and data used with their current installation.

Note:
This is a different question than asking whether existing projects and data will be compatible with a different version of ArcGIS Desktop, which has been well documented in release notes.

The uninstall or repair process for ArcGIS Desktop applications modifies the application files stored in "C:\Program Files" or "C:\Program Files (x86)". This means contents in the "C:\Users\<username>\Documents\" and "C:\Users\<username>\AppData" subdirectories is not modified or deleted, and all existing contents in those subdirectories are preserved.

By default, ArcGIS Desktop's application files are stored in "C:\Program Files" or "C:\Program Files (x86)". By default, user's projects and data are stored in "C:\Users\<username>\Documents\", which is a unique folder created for each user profile on that computer. For example, Joe's projects and data are stored inside "C:\Users\Joe\Documents", while Jane's projects and data are stored in "C:\Users\Jane\Documents").

User-specific application preferences are stored by default in the "C:\Users\<username>\AppData\Roaming\ESRI" and "C:\Users\<username>\AppData\Local\ESRI" folders. These folders in the \AppData subdirectory contain files related to Favorite items, Styles, Caches, Service Definition drafts, and various log files.

Note:
The "C:\Users\<username>\AppData\Roaming\ESRI" and "C:\Users\<username>\AppData\Local\ESRI" subdirectories store user-specific application preferences. To avoid loss of these preferences and a potential impact on the user experience of ArcGIS Desktop, it is recommended to rename rather than delete these folders when performing a clean uninstall of ArcGIS Desktop. Renaming, rather than deleting, these folders allows for restoration of application Favorites and Styles after the uninstall/repair process. 

Deleting the contents in the  "C:\Users\<username>\AppData\Roaming\ESRI" and "C:\Users\<username>\AppData\Local\ESRI" subdirectories will not modify user's data or projects.