Clothes often fit better when altered. Some might say that for images too. Two major categories of alteration for images are filters and transforms.
Most filters can be applied nondestructively to Smart Objects, and all filters can be applied to ordinary layers. Some filters are elaborate software and may require preparation, whereas others are super-simple. I will attempt to list many of them by general intention. That said, wonderful creative opportunities come from using features in unintended ways.
To scale, rotate, twist, bend, or distort images, we have an array of transformative tools, commands, and filters. Most of them are worthy of mention too.