Mainly anything that required an Xbox Live connection will be unusable. I did a while back using a very old version of Minecraft Windows 10 edition on Xbox and it loaded, worlds and all (even servers!) due to the lack of a requirement for Xbox Live.
I think it's anywhere before 0.15.0 or...
I've been playing fallout4 all day, I went into a elevator and it kept going, never stopped, waited 5 minutes, must of been a bug. How bout you, whatcha do today?