Before you crop out parts of a photo, or choose not to do so, why not think it out?
When taking a photo (or drawing or painting): First, decide on an emotion or an idea you’re trying to show: fear, anger, loneliness, balance, variations on a theme, darkness, mystery. Second, identify what part of your image most strongly makes this obvious: A scowl on a face? A misty moutain over a dark lake? Birds soaring free of constraints? Totally dejected and drooping body language? Third, add something unexpected or jarring or off balance so your viewer pays attention through the clutter and distractions of his or her life.
Then, last, chop away at boring things that don’t support your objective. Do you really want a large empty sky? Why have so much foreground separating the viewer from that thing or person you’re focused on? Is all the ‘stuff’ behind the back of that person really needed or does it just make folks wonder: ‘Why’s that all there?’
Think of it this way, would you like to see this?
In fairness, if you were in Nice, France, wanted to show how empty and clean your beaches are (photo: Blue Beach), you would not crop the foreground in the first of these two images. You might crop more of the sky (“Same sky as everywhere. So what?”). You might chop that lone person over on the right. (“Is that a woman or man? What is she/he doing?”). You wouldn’t crop the bottom, though. You want your viewer to *notice* the sand!
On the second photo, a bit more ‘artistic’, you want people to look at that bottle and its strange coloring. You chop off a lot of that irrelevant wood thing on the left, leaving just a bit of it. Why? To provide another group of browns to trick the mind into seeing the browns in that bottle and not just the greens.
See? It’s a lot about what you trying to do!