Why does Gparted leave a spare used space after formating for all File Systems(ntfs,fat32,ex4)?

I have maybe a theoretical question about file system or about gParted.

After when I deleted and then format into some file systems(ntfs, fat32, ex4). I noticed that some spaces are still in used on a different file system. Please take a look:

gParted did formatation on disks

If you have explaining video or wiki page about this and its background or you know could you please describe it below – then I may adjust the title of the question to later if somebody is curious about this.