Quick Look is, well, quick...and great

QuickLook:  an advance preview of an icon or image without opening up the parent program to see it, thus saving time and effort.

I tend to do alot of screenshots to save images as PNGs to review later or save as information for use later [as in showing someone how a certain file structure or window should look if you're explaining to them a process].  Thus, every now and then I do have to go thru and clean off the desktop of my computer.  I have all sorts of 'Picture #.pngs' all over and there's really no reason to keep them.  So, I open QuickLook [keystroke:  click on an icon and hit Command & Y - to close it do the same keystroke] and see what the icon represents and either delete it [just hit Command & Delete/Backspace while it's open in QL] and then click onto the next icon, without opening or shutting QuickLook.  That icon will then pop up so you can see it also.

You can even do a screen shot of the item you just opened in QL, not sure why you'd do that but it's interesting to know.  The only drawback to QL is that if you are in QL you can't keep that QL window open in QL when you move to an actual applications item or open window, it'll disappear.  But you can of course open the icon you just had up and look at both then.  So that would work.