Level of Detail is something that you can use to speed up the performance of Inventor. You can create different level of details with suppressed components(for example) that arent needed for the current operations/view or whatever.
The error you get in regards to associativity probably has to do with the current model view. For instance if you create a view that is your current model view in the assembly, being associative means that if you go back to the assembly, rotate the parts, your drawing will update. If you remove associativity, it will not.