The variable aperture still feels a bit gimmicky to me. I prefer a larger 1" sensor over this.
The variable aperture is most useful when recording videos.
When shooting video on a phone, the automatic adjustment of the shutter speed results in sharp and unnatural edges.
For video to portray motion in a way that feels natural to the human eye, it is recommended to adhere to the 180-degree rule. This means that the shutter speed should be set to twice your frame rate, resulting in a video with some motion blur which makes the footage look more authentic.
So, with Xiaomi's auto variable aperture feature, you can lock the shutter to 1/60th when shooting at 30fps or 1/120th when shooting at 60fps to achieve a smooth high-end cinematic look.
If your phone camera doesn't allow you to adjust the aperture, locking the shutter speed can result in a video that is too bright, as it is letting in too much light in. In such cases, you can use an ND filter attachment to lower the exposure level.
Yes, you can also fix the sharp look in post-production but it is always best to get it right in the first place to avoid any video artifacts.
Of course, if you want to have the best sensor, you need to wait for the 14 Ultra.