Stuff can break when you update engine versions. It's not really a problem for hobbyists who never ship anything, or games that are early in development, but I guess in Shenmue III's case YSnet would have to see if updating would be worth blocking out the time to fix the parts that fuck up.
There's also apparently differences in how things can break depending on if your project is made in Blueprints, or using C++, but I've got no idea which way that stuff swings. Could make things easier, could make things harder.
WildManofBorneo wrote:I was thinking more along the line of the lighting enhancement features in 4.18 such as the new Volumetric Lightmaps and Improved Static Skylight Directionality.
Ahhhh, I thought you were strictly talking about 4.19.
The improvements you're talking about might not be applicable with Shenmue III because of the day/night cycle, though. Going by the examples on the UE blog it looks like they're mainly for games that use baked lighting, but I dunno enough about UE4 to say for certain.