We field a lot of support requests, and similar to a doctor's office, we see some extreme cases. One of those interesting extreme cases are folders with high file counts. Any time a folder has more than a few thousand items in it, the filesystem is going to be a lot slower when working with that folder. Adding a new file, for example, requires that the filesystem compare the new item name to the name of every other file in the folder to check for conflicts, so trivial tasks like that will take progressively longer as the file count increases.
