There are two versons BleachBit and BleachBit(root)

Forums: 

why?

Running BleachBit as a normal user is for cleaning your user profile, such as system cache and web browsers.

Running as root grants extra privileges to clean the system-owned files and data, such as system logs, localizations, and package managers cache.

Which you choose depends on what you want to clean.

See also the Frequently Asked Questions.

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Andrew, lead developer