By default, CrashPlan backs up everything in your home folder including all hidden directories (directories starting with a dot (.). This would include some directories your probably don’t want backed up, such as ~/.local/share/Trash (your trash) and a bunch of other hidden directories.
Fortunately CrashPlan’s file exclusion feature includes a way to specify exclusions by regular expression. Simply go to Settings > Backup and next to Filename Exclusions click the configure button.
Check the box for Regular Expression and enter this:
.*/..*
Click the plus sign, then ok, then save again.
That will exclude all the dotted directories from your backups.
Reference: CrashPlan Support – Using Regular Expressions (regex)
Have any filename exclusions that you use on your backups? Feel free to share your rationale in the comments below!