My phone (XA2 4.4) memory was getting full.
Then i noticed that erasing the thumbnails freed about 6GB of memory!
in /home/nemo/.cache/org.nemomobile/thumnails are a loooot of pictures from either sailfish apps (fernschreiber) either thumbnails of photos taken and later erased.
Keeping those photos is an issue with storage and privacy.
I wonder if jolla would consider cleaning this cache for exemple during each upgrade?