when I export fbx from a model, it has 27 Mb size but the file that enscape creates after saving asset has 85 Mb size (the file format with .Bin Suffix )
File size depends on the file format. Enscape uses .gltf which sacrifices file size for loading and rendering speed (this is a great oversimplification).
That the file size is larger does not mean that the model is automatically more or less detailed or ‘heavier’ to load, all it means is that it takes more room on your file storage.