There's no rules about tilting your camera. I normally tilt when I think that it will add to the image e.g leading lines to the subjects or conveying movement. Images like landscape, the horizon should be straight so tilting is not advisable. Of course there are always exceptional cases. Also tilting is like adding spices to the soup. 1 or 2 to add flavour but if you have too many images of the same tilt, it will become boring.
There are plenty of creativity to shoot off axis or intentionally slant the horizon depending on what the photog is trying to communicate, and thus it can be a creative addition to drawing positive attention - it will be up to the audience to judge the success / failure.
However there are certain genres such as wide panoramic landscapes that many would still prefer the traditional leveling , and even a little slant by a degree or two can be a biting eye sore.
Subjectivity although often mentioned, should not be an excuse for carelessness.
Depending on the content. For example, in events it may not be possible to think, plan and decide which angle to tilt ALL The Time. By the time you decide, the moment is gone and will never come back. A lot of time, base on developed personal style and perhaps gut feel.