A really useful application is https://wiki.gnome.org/action/show/Apps/DiskUsageAnalyzer?action=show&redirect=Apps%2FBaobab
When you are looking for free space, you can easily find where big files are stored.
I love to use it on my desktop, but I would love to have something similar on nextcloud as sometime we don’t synchronize all files.
User mode: See easily the usage of your files.
Admin mode: See easily what your users are using.