I’m going to agree partially with the first answer. I’m not sure about the multiplayer part as I don’t know enough about UE4 to answer that, but to answer your question, it depends. World composition is very helpful if you plan on having detailed landscapes with a lot of foliage, props, actors, etc. This is mainly due to performance issues, as loading an 8km map at once not only takes a while, but depending on what you have in that map, it could perform very poorly.
If you are using a lot of low poly assets with simple materials and don’t plan on having an abundance of props in your world, then no, you do not need to use world composition, but otherwise, yes. Think about it this way: If your game is something you could see running on a PlayStation 2 / original Xbox or better (graphics wise), that means you’ll need world composition because otherwise, even with effective use of LODs, you’re going to have far too many polys on screen and way to many draw calls from shaders, not to mention any active AI you might have, any gaming console is going to run at around 2 FPS, and anything short of a future proof gaming PC is too.
I’m not going to lie to you, if you’re new to UE4 or have never used world composition before, it will be imposing, and setting up everything you need is a pain. I am pretty new to everything myself and am kind of struggling with some aspects of world comp, but if you need any help, I’ll do what I can. I’m going to include the most useful links I’ve found on world composition.
The is the official epic games livestream which is really useful as a start. They do use World Machine (which is totally worth it, but not required) A good alternative is terrain.party which is shown in the video. The one thing you have to make sure about is to use a size which works with UE4. The next link is to the landscape technical guide which shows the recommended sizes which (I believe) are all working with world comp. Pro tip, use smaller sizes (505 is what I’m working with).
One thing about this page, it says to make sure “flip y axis” is ticked. You don’t have to do that anymore if you tick the one with the same (similar) name in the import tiled landscape in UE4.
I found both of these pretty helpful as well.
Most of this information is useful if you’re using landscapes. If you’re not, it becomes less useful, but world composition is still something I’d recommend.
Best of luck.