Why YSK: I’ve been seeing an increasing number of phone photos shared online in 9:16, 9:21 or similarly tall aspect ratios, often with parts of the subject cut off. I’ve asked a few people why they cropped their images that way, and none of them knew they were cropped.
Sure, pre-cropping is a valid technique, best done intentionally.
Dedicated cameras intended for photography (rather than videography) almost exclusively come in either 4:3 or 3:2. Video cameras occasionally use 16:9, or even weirder ratios.