If nothing ever comes of it, it doesn't matter either way. If it becomes successful enough to launch into its own company, there is a huge disadvantage to not

If nothing ever comes of it, it doesn't matter either way. If it becomes successful enough to launch into its own company, there is a huge disadvantage to not having the IP situation clarified up front. For one thing, investors get very concerned about even the remote possibility of someone else trying to claim copyright to your code. And once you are successful, it's not safe (or ethical, really) to just assume your [former] employer will never hear about it and connect the dots.