Cropping for better composition

Cropping is an editing feature that allows you to trim off parts of the image that you don't like—it provides an opportunity to recompose the shot after it has been taken.

However, one vital point to remember is that cropping discards pixels and therefore 
lowers file resolution. I love photographing birds, but unfortunately, they always tend to 
be too far away, even with a 400 mm telephoto lens, so I have to crop the edges off the file 
to make the subject appear larger. If I crop 50% from a photo, it then looks as if I have shot the subject with an 800 mm lens, not my regular 400 mm lens. Cropping has saved me a lot of money in my not having to buy an even more powerful (and thus very expensive) lens. But the inevitable compromise is that, in that example, I have lost half the pixels in the 
file—no problem if I only ever post the image online, but a restriction if I hope to have 
it printed...