Slow expanding subdirectories. Too many files?

It sometimes takes a long time to expand a subdirectory, using a lot of CPU. Is there a way I can rearrange my subdirectories to avoid this?

Perhaps I need to push sub subdirectories with a lot of files in them deeper? How many levels does it scan when it expands? Does it scan the entire tree, or just 1 or 2 levels deep?

I have one directory with 244 subdirectories & 3 files. The subdirectories mostly have around 5 files and 2 directories. One has 356 files and 4 directories. Another has 208 files and 2 directories. Some of the deeper directories have quite a few files in them.

Does this happen in Explorer as well as Opus?

If it's only happening in Opus, see the FAQ on slowdowns when entering certain folders for a list of things that may be causing it (e.g. video codecs that go wrong with certain files can cause it).

Sub-directories have no effect at all when listing parent directories, unless you have something switched on which causes sub-directories to be scanned. (For example, turning on automatic folder-size calculation or the columns which show number of sub-files/folders will obviously cause Opus to scan all sub-folders. And in Thumbnails mode folder thumbnails will look at a few files in each folder to generate a thumbnail for the folder (unless folder thumbnails are switched off).)