One of the things that can eat up storage space quickly is your thumbnails.
If you have a computer running all the time in your house, you can redirect the thumbnails to this computer. If you have multiple Kodi devices you can share this location so you don't have to have a copy of all the thumbnails on all your devices. This requires modifying the advanced xml file. See the Kodi Wiki for details on this. Add the following to the xml file.
For Android Devices:
<substitute>
<from>/storage/emulated/0/Android/data/org.xbmc.kodi/files/.kodi/userdata/Thumbnails/</from>
<to>smb://NAS/kodi/userdata/thumbs/</to> <!-- YOUR NETWORK PATH TO THIS FOLDER: This folder is where the thumbnails will be stored-->
</substitute>
<substitute>
<from>/storage/emulated/0/Android/data/org.xbmc.kodi/files/.kodi/userdata/sources.xml</from>
<to>smb://NAS/kodi/userdata/sources.xml</to> <!-- YOUR NETWORK PATH TO THIS FILE: This file is optional to keep your sources in sync with all your devices-->
</substitute>
<substitute>
<from>/storage/emulated/0/Android/data/org.xbmc.kodi/files/.kodi/userdata/mediasources.xml</from>
<to>smb://NAS/kodi/userdata/mediasources.xml</to> <!-- YOUR NETWORK PATH TO THIS FILE: This file is optional to keep your media sources in sync with all your devices-->
</substitute>
For Windows:
<substitute>
<from>special://profile/Thumbnails/</from>
<to>smb://NAS/kodi/userdata/thumbs/</to> <!-- YOUR NETWORK PATH TO THIS FOLDER: This folder is where the thumbnails will be stored-->
</substitute>
<substitute>
<from>special://profile/sources.xml</from>
<to>smb://NAS/kodi/userdata/sources.xml</to> <!-- YOUR NETWORK PATH TO THIS FILE: This file is optional to keep your sources in sync with all your devices-->
</substitute>
<substitute>
<from>special://profile/mediasources.xml</from>
<to>smb://NAS/kodi/userdata/mediasources.xml</to> <!-- YOUR NETWORK PATH TO THIS FILE: This file is optional to keep your media sources in sync with all your devices-->
</substitute>
If you have a computer running all the time in your house, you can redirect the thumbnails to this computer. If you have multiple Kodi devices you can share this location so you don't have to have a copy of all the thumbnails on all your devices. This requires modifying the advanced xml file. See the Kodi Wiki for details on this. Add the following to the xml file.
For Android Devices:
<substitute>
<from>/storage/emulated/0/Android/data/org.xbmc.kodi/files/.kodi/userdata/Thumbnails/</from>
<to>smb://NAS/kodi/userdata/thumbs/</to> <!-- YOUR NETWORK PATH TO THIS FOLDER: This folder is where the thumbnails will be stored-->
</substitute>
<substitute>
<from>/storage/emulated/0/Android/data/org.xbmc.kodi/files/.kodi/userdata/sources.xml</from>
<to>smb://NAS/kodi/userdata/sources.xml</to> <!-- YOUR NETWORK PATH TO THIS FILE: This file is optional to keep your sources in sync with all your devices-->
</substitute>
<substitute>
<from>/storage/emulated/0/Android/data/org.xbmc.kodi/files/.kodi/userdata/mediasources.xml</from>
<to>smb://NAS/kodi/userdata/mediasources.xml</to> <!-- YOUR NETWORK PATH TO THIS FILE: This file is optional to keep your media sources in sync with all your devices-->
</substitute>
For Windows:
<substitute>
<from>special://profile/Thumbnails/</from>
<to>smb://NAS/kodi/userdata/thumbs/</to> <!-- YOUR NETWORK PATH TO THIS FOLDER: This folder is where the thumbnails will be stored-->
</substitute>
<substitute>
<from>special://profile/sources.xml</from>
<to>smb://NAS/kodi/userdata/sources.xml</to> <!-- YOUR NETWORK PATH TO THIS FILE: This file is optional to keep your sources in sync with all your devices-->
</substitute>
<substitute>
<from>special://profile/mediasources.xml</from>
<to>smb://NAS/kodi/userdata/mediasources.xml</to> <!-- YOUR NETWORK PATH TO THIS FILE: This file is optional to keep your media sources in sync with all your devices-->
</substitute>