On original rims of manufacturer recommended size and offset, there are no downsides.
On Chinese, Taiwanese, so called Thai rims we buy from local market the rim is heavier than same size steel rim so it affects suspension, performance and fuel economy and only purpose is cosmetics.
Meanwhile factory alloy rims are lighter than steel rims and have positive affect on above factors, the 16" if not lighter would be at least around same weight as stock steel rims.