iCleaner can free up space by removing unnecessary files from your device. The cleanup process is made of the following steps:

Message attachments

It deletes files sent and received via iMessage or MMS. The "smart" setting only deletes files that do not show up in any message, while "on" deletes all attachments (messages with attachments will show a blank icon).

Safari

It deletes cookies, browsing history and cache files to free up memory and preserve your privacy.

Applications

It deletes App Store app caches, cookies, temporary files and snapshots. Furthermore, it detects popular applications for a more in-depth cleanup.

More apps are added with each subsequent release. User data, useful cookies and other relevant files are left untouched.

OTA software updates

It deletes downloaded iOS update files.

Battery usage data

It deletes archived battery data, while leaving current battery data untouched.

Cydia

It deletes Cydia caches and temporary files, cache files generated by Cydia apps and tweaks, partially downloaded packages and repo files.

Cydia sources

If you enable this step, Cydia will not list any package until it reloads the package lists. This is disabled by default since it's only helpful when Cydia sources aren't updating correctly due to corrupt lists.

Note that this does not delete the Cydia repositories you added. Rather, it forcefully purges their local package lists.

Unused dependencies

It issues the apt-get autoremove command in order to remove packages installed as dependencies that are not needed anymore, and purges uninstalled packages.

This is disabled by default since it should only be used by experienced users who want to automate the operation. Note that removed packages and preferences are not included in the "analyze" filesize count.

Log files

It deletes log files and crash reports from known locations. These files are generally irrelevant to the user and can be safely deleted.

Cache files

It scans and deletes system cache files and databases. Some of them are rebuilt upon respring. This helps removing obsolete cache data.

Temporary files

It deletes temporary files from your device. These files are meant to be removed automatically, but they often happen not to.

Filetype cleanup

iCleaner features a custom cleanup pass based on file extensions. By default, it looks for log and temp files all over the directory tree.

You may want to add more extensions (such as "bak" or "old"), but use this functionality with caution.

Also, note that iCleaner will not allow you to use most non-alphanumeric characters and some disallowed extensions (disallowed ones will be removed as you confirm).

Custom files and folders (Pro version only)

With this extremely powerful feature, you can add any file or folder to the cleanup process. Tap on "Add item" to add a new item to the cleanup, or an existing item to edit it.

Please use this with caution, as accidentally deleting critical files can force you to restore your device.

Read more about the custom cleanup configuration fields.

You can tap on a specific cleanup step to quickly perform its analysis or cleanup.