If you work with large Photoshop files, you’re probably well aware of how slowly they save. Much of that time is spent flattening your image in order to create the preview icon you see in the Finder. While useful to have, you probably don’t need to see a preview icon for every interim version of your image. By disabling preview icon generation on save, Photoshop will save your work much more quickly. You can change how Photoshop works permanently via its preferences, or just on a save-by-save basis.
To permanently alter Photoshop’s preview icon behavior, select Photoshop -> Preferences -> File Handling, and look in the File Saving Options section. Set the Image Previews pop-up to Never Save if you want to permanently banish icon previews, though that will make browsing your images in the Finder much tougher. A better option is to select Ask When Saving. When you save a file in the future, you’ll see a new section in the Save dialog that lets you enable or disable the preview for that particular save.
If you’d rather not make a permanent change, here’s a workaround that will accomplish the same result. Create a new group (Layer -> New -> Group) and call it Toggle All or Master Group or something similar. Now drag all your existing layers and groups into this new group. When you want to save quickly, without a preview, turn off the visibility to this Toggle All group (click the small eye icon in the Layers palette), then save. If you want the icon previews created, leave the visibility as it is prior to saving.
A non-group alternative method of doing the same thing is to Option-Click on the eye icon for any one layer, which will hide all layers other than the selected one, then release the Option key and click the eye again for that same layer, hiding that one. After you save the file without the preview, the quickest way to show all the hidden layers is to control-click on the Layers palette and use the contextual menu.
This trick won’t make much of a difference on smaller Photoshop images. But if you routinely work with large, multi-layer, multi-group masterpiece, the time savings can be considerable.