In my case, it depends on what I'm holding as to whether I use inserts or nuts. Anything that has a load with any tension gets nuts. Since an insert doesn't really make a bolt/screw install any stronger, other than making the threads themselves more durable, I only use them in non-loaded or 90 degree load situations. Since I build boats as well, the only place I use inserts is in the transoms as drains or in the case of winged boats, in the ends of the wing for the nylon retaining screws.