It sounds like a nice feature but in my experience such "auto-magic", always-on features can burn battery life. It's not necessarily much for each single feature but there are so many of them these days, they add up quickly.
The other downside is false positives or other occasional failure modes. Many such "auto-magic" features choose not to expose any granularity to the user, perhaps because they think it'll make it less "magic" or that a few entirely optional scaling settings in an "advanced" tab will hopelessly confuse users. Too often such "all or nothing" reliance on the infallibility of their magic 'do-the-right-thing' code forces me to entirely turn off what would otherwise have been a useful feature.
The other downside is false positives or other occasional failure modes. Many such "auto-magic" features choose not to expose any granularity to the user, perhaps because they think it'll make it less "magic" or that a few entirely optional scaling settings in an "advanced" tab will hopelessly confuse users. Too often such "all or nothing" reliance on the infallibility of their magic 'do-the-right-thing' code forces me to entirely turn off what would otherwise have been a useful feature.