The one of the reasons I don't do this in inventor is because of how many extra things end up being on my screen when I have a part opened inside of an assembly. I go to make a sketch and its grabbing all sorts of stuff that I don't want involved with the features inside the part. I also have a lot of parts that get reused, and actually I'm not sure, when you start a new part within the context of an assembly, is it's origins relative to the assembly origin, or is it entirely independent of the assemblies origin.
Now using a program like solid edge, I have no problem creating and editing parts within the context of an assembly. Inventor makes it so **** difficult to see things when youre in an assembly. Every time I want to just make something disappear so I can see past it, it wants me to either remove associativity or modify a design view representation(which I really don't know what that even means really), when I should be able to just make it visibile or invisible without any modifications to any files being necessary whatsoever. And I should be able to have an assembly open, go into a part and hide the previous levels of assemblies so I don't have to deal with all the dang lines from the other components in the assembly. Also should be able to dimension to quadrants, shouldn't have to project any geometry from edges in a part just to dimension from them, and shouldn't have to place a point at the midpoint of anything to dimension to the midpoint. Also, there should be a normal cutout.