the softwares fill up free spaces with logs and unwanted junk.
if you want to enjoy your phone like new,
take backup
do a complete format.
do restore.
less free space is major issue for phone slowing down., and some major companies give 16 gb for internal storage .
and reboot your phone once in a two days. it keeps phone fast, at least in my case.
It can still be that RAM is full, it happens when you use the Internet. Except for all files in the phone there are additional, which the owner does not see, but they must also be deleted by the cleaner.