That's literally how any update on a computer ever will work. Real downsides worth mentioning would be like "you'll be unbootable, you can't rollback, it'll update a bunch of other packages, it might delete user home". Having to select an old entry in your grub config at boot because the new kernel doesn't play nice with any number of custom peripherals or packages on your system is not what I would consider a serious downside and you'd have to do it if Kubuntu decided to roll a kernel update anyway. Do you uh, use linux?