Sometimes, you may want to use a tilted angle for creative effect. If you choose to slant the horizon, make it fairly obvious or it may be mistaken for sloppy framing.
One day, a hundred years from now, if this picture hang on the wall of some art gallery, an arty-farty visitor will speculate:
“The photographer wanted to convey the contrasting perspectives of urban and rural, the clash between development and conservation. The two sets of twins represent abstract symmetry but the oblique angle is a subtext of the underlying conflict…”
Actually, the reason I used the Dutch Angle here was pedestrian. I wanted to keep both the skyscrapers and the banana tree in Kampung Baru within a a single frame There was simply no space for me to move back for a more conventional framing.
Olympus OM-D, ISO 200, f11, 1/320 sec.