Lots of ink has been spilled about this but many of the solutions given, such as installing 3rd party cleaner apps or filling your disk space with empty files, are terrible. You just need this terminal command:

sudo /System/Library/Filesystems/apfs.fs/Contents/Resources/apfs.util -P -high ~

It freed nearly 250GB of space on my machine after several minutes. If anyone knows how to tune the threshold at which this happens automatically I’d love to know. Until then this works at cleaning it up when problems arise.