A nice free light app to monitor your disk usage by folder is this WinDirStat:
https://windirstat.net/ On start up, it reads the whole directory tree once and then presents it in three useful views:
- The directory list, which resembles the tree view of the Windows Explorer but is sorted by file/subtree size,
- The treemap, which shows the whole contents of the directory tree straight away,
- The extension list, which serves as a legend and shows statistics about the file types.
I really gotta wonder why Microsoft doesn't include something like this in the basic Windows accessories...