Like gaucho777, I use them differently depending oh the bike. Derailleur function, wheeelbase and fender clearances are factor in. So does having excess screw exposed. Now, on my commuter fix gear, I set it to accurately set the chain tension and make for quick wheel installs in the dark, cold or wet.

(My good fix gear was built to accommodate the screws but I found that the technique of pulling the wheel back with my left hand on the left chainstay and pulling the tire over to hit it, then tightening the right axle nut worked so well to get the chain tension right that I scrapped the screws. This requires an accurate and round crankset and rings. Thank you, Sugino 75, for making my life easier.)

Ben