This becomes especially apparent on slow storage devices such as image DVDs or slow hard drives. You will notice that the loading is faster when the thumbnail cache is enabled.
The effect that a thumbs.db cache file and thumbcache file has on the loading time of a folder can be witnessed best if you open a large folder full of image files. While one of the main purposes is to process jpeg, png, bmp, tiff and gif image files, the cache is also used for document formats such as docx, pptx, pdf and html, and video formats such as avi. Windows does not only store image formats in the database files though. Without the thumbnail cache, Windows would have to process the images in the folder on load every time the folder is opened, which can slow down the display depending on the overall performance of the system and the number of image files in the folder.
