During the lifetime of a typical computer, many folders are static in their contents. For example, a program like Matlab, loaded with some toolboxes, is installed once and seldom changes ever after. It takes a large amount of disk space, but more importantly, it contains thousands of small files.
These folders substantially slow down the WinDirStat file tree scan.
The utility's interface allows to scan subtrees. But can you exclude a subtree while scanning its parent tree?