Limitations for importing assets to UEFN.

So, in the documentation explaining how to import assets it says “If the total file size of all assets exceeds 256 MB, you will not be able to deploy the level to Fortnite Creative.”. What does this mean exactly? Does it mean that I would have to work always with the Unreal Editor but I can later publish my island to the game?

Whenever y want to test my project I’m taken to a creative session where I can then start the game, how would the testing flow be in case that I cannot publish to creative but still create the island?

Thanks