When you don't understand where your disk space is disapearing check:

Library/developer folder
local snapshots for time machine (even if it is disabled!)

A single time machine local snapshot can take 5Go to 10Go disk space (for example after a huge MacOS or Xcode update).

It is often said that disibling timemachine should trigger a cleaning from the system. But this is not true, at least in my experience (on macOS High Sierra).

recovering space from time machine local snpashot

List all local snapshots adding their dates as detail

tmutil listlocalsnapshotdates /

If there are some local snapshots on your Mac, something like this should be answered:

Snapshot dates for disk /:
2017–10–04–204856
2017–10–07–062421
2017–10–07–162926

Otherwise just this line:

Snapshot dates for disk /:

Delete a local snapshot by date

tmutil deletelocalsnapshots 2017–10–04–204856
Deleted local snapshot ‘2017–10–04–204856’

Deleting these 3 snapshots made me recover 15Go disk space on my Mac.