By default, CrashPlan backs up your User folder, which contains the AppData folder for your Windows computer. Files in this folder update quickly. Consequently, your backup may not be reaching 100% if this folder is kept in your backup set. This article explains what the AppData folder is so that you can determine whether you want to keep it in your file selection.
AppData is a hidden folder located in C:\Users\YourUsername\AppData\. The AppData folder contains custom settings and other information needed by applications. For example, you might find the following in your AppData folder:
Certain files inside AppData can fail to back up with CrashPlan. When this happens, your email reports show less than 100% backed up, and CrashPlan's History log displays the message "unable to backup X files." This happens because the files in this folder:
C:\Users\YourUsername\AppData\Local\Microsoft\Windows\Notifications\WPNPRMRY.tmp C:\Users\YourUsername\AppData\Local\Microsoft\Windows\UsrClass.dat.LOG1 C:\Users\YourUsername\AppData\Local\Microsoft\Windows\UsrClass.dat.LOG2 C:\Users\YourUsername\AppData\Local\Microsoft\Windows\WebCache\WebCacheV01.dat C:\Users\YourUsername\AppData\Roaming\Skype\your.skypename\main.lock C:\Users\YourUsername\AppData\Local\Google\Drive\lockfile C:\Users\YourUsername\AppData\Local\Microsoft\Internet Explorer\Recovery\High\Active*.dat C:\Users\YourUsername\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>.default\parent.lock C:\Users\YourUsername\AppData\Local\Google\Chrome\User Data\Default\Current Session C:\Users\YourUsername\AppData\Local\Google\Chrome\User Data\Default\Current Tabs C:\Users\YourUsername\AppData\Local\Google\Chrome\User Data\lockfile
It's up to you. Because most applications only store their configurations settings, not files you create, in this folder, it's often not important to back it up. However, there are exceptions to that rule--most notably older versions of Outlook (see below).
If you decide to change your file selection to remove the AppData folder, there are a few things to keep in mind:
Versions of Outlook prior to Outlook 2010 stored your PST files (a.k.a. Personal Folders, commonly used for archiving mail) in: C:\Users\YourUsername\AppData\Local\Microsoft\Outlook\
However, later versions store PST files in C:\Users\YourUsername\Documents\Outlook Files\, which CrashPlan backs up with the rest of your Documents folder.
If you're not sure where your Outlook PSTs are located, see this article from Microsoft: "How to locate, move, or back up your personal folders (.pst) file in Outlook"