What is it? Smart Objects is a way to preserve the full resolution quality of your image and resize it in your document. This way you don’t destroy any information that you originally had with your image.
How do you use it? You can find this option in your tool bar: Layers>Smart Objects>Convert to Smart Object OR right click the layer that you want to convert and select Convert to Smart Object. When it is converted you will see a little symbol appear at the bottom right corner.
Where do we use it? This is a great way for us to make our website layouts. It gives us a way to resize images on a page to make the best possible arrangement without having to depreciate our image resolution. Furthermore, we can change our layout in the future if we want to pair it with another image or make it larger on our canvas.
Just a reminder that your image file size stays the same because it stores the original image file.
Image credit: Glen Luchford