I recently upgraded from a 2019 Intel Mac to a similarly-specced M3 Mac, and it really is night and day. My battery life is more than doubled - I can run IntelliJ and multiple Docker containers on battery for more than my whole work day, when before it would barely last a couple hours with that load and be slow while doing so. The fan hardly ever runs while on my Intel Mac it would run constantly.
I recently upgraded from a 2019 Intel Mac to a similarly-specced M3 Mac, and it really is night and day. My battery life is more than doubled - I can run IntelliJ and multiple Docker containers on battery for more than my whole work day, when before it would barely last a couple hours with that load and be slow while doing so. The fan hardly ever runs while on my Intel Mac it would run constantly.