I have my units set to 8 decimal places, or 256ths if using architectural units. Not because I ever intend to go to such extremes when creating drawings. But rather because for me one of the primary qualities of cad is the precision involved. There's no sense in my opinion in being casual with the numbers when you can be purposeful. I'm also compulsive about things, so I tend to quibble even when it isn't necessary.
One other thing that has changed my perspective a bit as well is diving into machining as a discipline and potential vocation. In machining terms, a 64th is almost 16 thou, 5 thou would be a generous tolerance in many cases. You might as well be doing carpentry at that point if those are the standards you're working to!!!
I presume you're talking about snapping to a grid with this comment? If so, I never ever have the snap on, unless by accident, as it's next to the F8 ortho toggle function key and I sometimes hit F9 by mistake. I prefer to simply draw things as they are meant to be, as Autocad supports the dynamic entry of distances and angles within nearly all drawing and editing commands. It's really quite simple.
Also, it's quite simple to switch from imperial to metric even if the drawing has been started in the opposite style. The "dwgunits" command will walk you through it.
Jim (US).....should change all of my users names across multiple forums to this....