The beta version is used to collect bugs, so it may be buggy and unstable.
To avoid your data loss, you should always backup your User Data before trying any beta version.
By the way, these directories including their subdirectories can be deleted freely without any harm:
User Data\<ProfileName>\Application Cache
User Data\<ProfileName>\Cache
User Data\<ProfileName>\GPUCache
User Data\<ProfileName>\JumpListIcons
User Data\<ProfileName>\JumpListIconsOld
User Data\<ProfileName>\Media Cache
User Data\<ProfileName>\Pepper Data
Generally, your default profile name is "Default".
JumpListIcons contains your most visited links(right click taskbar icon to see them), maybe some users want to keep it.
To avoid your data loss, you should always backup your User Data before trying any beta version.
By the way, these directories including their subdirectories can be deleted freely without any harm:
User Data\<ProfileName>\Application Cache
User Data\<ProfileName>\Cache
User Data\<ProfileName>\GPUCache
User Data\<ProfileName>\JumpListIcons
User Data\<ProfileName>\JumpListIconsOld
User Data\<ProfileName>\Media Cache
User Data\<ProfileName>\Pepper Data
Generally, your default profile name is "Default".
JumpListIcons contains your most visited links(right click taskbar icon to see them), maybe some users want to keep it.