We can view thumbnails of jpg, png, tiff or any other image files in windows explorer. Thumbnails helps in selecting proper image file for any task. However windows can’t generate thumbnail of Adobe Photoshop psd & Adobe Illustrator eps files.
The users like Graphics designer and web developers who need to often work on Photoshop like tools for them it becomes difficult to select psd & eps files since you don’t know content of the file unless you actually open with respective applications.
Here is very useful addon, PS+Ai Thumbs which shows Photoshop (PSD) and Illustrator (EPS) file thumbnails in Explorer (only in thumbnails view).