There will always be that one "smart-a*s" person, who tries to use old stuff that wasn't shared before, like the game they've been working on for X months but didn't share it on social media. If you want to secure yourself and give possible haters (like watermark mentioned) nothing to hold against you... share your progress online, so people can see the game evolve in realtime and will not be like: "bah, you sure haven't done all this in only one month! NEVER EVER. Cry cry."
Because there are those people and there are those that cheat and really use project that they started months ago. Some of that might be hard to proof in the end.