Wow, amazing.
For me, the usual suspects are stuff like PlasmaConfigSaver - which bloats my config directory somewhat to about 8GiB…
Then podcasts (The Infinite Monkey Cage is 3.5GiB) and .cache is pretty big too…
But 250GiB system disk - not an issue. Wouldn’t be clever on a laptop without extra storage options though.
Hmmm one issue I have with ncdu / is that it includes my Timeshift (mounted /run/timeshift - where it’s also mounted by the system as /mnt/T3/timeshift and is a separate drive).
ncdu -x
. 40.6 GiB [##########] /home
. 20.0 GiB [#### ] /usr
. 15.5 GiB [### ] /var
8.0 GiB [# ] swapfile
3.5 GiB [ ] /opt
103.9 MiB [ ] /boot
. 17.7 MiB [ ] /etc
168.0 KiB [ ] file
24.0 KiB [ ] desktopfs-pkgs.txt
! 16.0 KiB [ ] /lost+found
12.0 KiB [ ] /srv
8.0 KiB [ ] rootfs-pkgs.txt
! 4.0 KiB [ ] /root
4.0 KiB [ ] /mnt
4.0 KiB [ ] .manjaro-tools
@ 0.0 B [ ] FileBot_4.9.3-aur.tar.xz
@ 0.0 B [ ] filebot.sh
@ 0.0 B [ ] sbin
@ 0.0 B [ ] lib64
@ 0.0 B [ ] lib
@ 0.0 B [ ] bin
> 0.0 B [ ] /tmp
> 0.0 B [ ] /sys
> 0.0 B [ ] /run
> 0.0 B [ ] /proc
> 0.0 B [ ] /dev
Ncdu Scan Options
These options affect the scanning progress and have no effect when importing directory information from a file.
-x
Do not cross filesystem boundaries, i.e. only count files and directories on the same filesystem as the directory being scanned.
84GiB
Red is /home
cyan is /usr - that’s 1/4 and the next cyan from that is office6
purple /var and 9GiB pacman cache
pink mostly Plex server.
So what did you add that takes up an extra 80GiB more than this?
So sure, ncdu is ncurses, so you go into your top 3 or so directories (that’s 76GiB of my 87.4GiB anyway) and poke around in there.
Certainly one game 0 A.D for me increased the bloat quite a lot. Also Plex is heavy on storage with huge caches.
For installed stuff, I do a clean every now and then
clean='paccache -rvuk0 && sudo journalctl --vacuum-time=2weeks'
Good luck 
Oh, and don’t forget to look in Timeshift and exclude some crud from there…
/var/lib/plex is a big one to remember. That would double my restore time (maybe a million mostly tiny files in there…)