Open Photoshop and open the image you want or need to crop.
To crop hit the C key of your keyboard. Make sure the content aware crop is selected.
Now crop the photo like you used to do it before.
Hit Enter to crop it. Photoshop will now try to fill the transparant parts. When you have a picture with skies etc it does a fab job.
When the photo has more content like buildings on the edges you might get some weird results, but with the clone tool (S) you can fix this. I think its an awesome function and very helpful.
You also can use it to add more sky or more pixels to either side of your image. Let's say you want to have more space at the bottom of this picture.
Use the content aware crop to do this.
Hit enter to crop it. Because the shoes are very close to the edge of the picture, the result is a bit weird.
But with the clone tool it's easy to fix.
Another way to avoid or reduce the strange results is to use a mask. Let me show you how this works. I'll use this image:
I crop it like this:
Enter the weird result: part of the lamp post in the middle of the sky.
The trick is to add a mask and paint with a hard black brush. Paint the part that seems off in the picture.
Now crop the picture again:
Voila! Now I got a much better result