As rubber ages, it gets harder. As rubber gets colder, it gets harder. So, the worst combination would be to have older tires (tread depth does matter, but not if it can't conform to the road surface) in cold weather. The stopping and cornering grip is measurably lower.
So, if you drive when it's below about 45F, or your tires are getting older, and you get into an emergency situation, it could be the difference between easily maneuvering around the problem, or stopping. Is that worth it for looks? The tread pattern on summer tires doesn't do well on ice or snow, either.
In some places in the world, not having the 'proper' tires would elicit a citation.
The i3 is sold all over the world...some places never get below the temperature where summer tires work. Also, in many parts of the northern world, it's common to own two sets of tires so that it can be optimized for both types of weather, and in some, it's mandatory. So, on the i3, 20" performance (summer) tires would allow the best of both seasons when the tires/wheels are optimized for the weather.
An all-season tire is a compromise, all seasons. A winter tire doesn't work well in hot weather. A summer tire doesn't work well in cold weather because that's how they're designed. An all-season tire works okay in all seasons, but does not excel in any.
2011 535i x-drive GT, 2014 i3 BEV
Soon (hopefully!) A 2021 X5 45e will replace the above