The only reasons the hex-head screw on the left-hand side of the axle is there is to a) help push the axle out of the fork pinch clamps, and b) help locate the axle properly before the pinch bolts are tightened. (There is an 'unseen' part to that, because tightening the right-hand pinch bolt and then tightening the hex-head screw will help remove any play between axle, wheel-bearing inner races, wheel-bearing spacer and outer wheel spacer.)
The only time you might have trouble getting the axle out without using an axle-removal tool is if the axle or forks are bent.
...But by that stage, you'll probably have bigger things to worry about.
To eliminate removal problems, make sure the axle is squeaky-clean, then give it a LIGHT smear of copper paste before re-installing. Wipe off any excess.
Once the axle has been properly centred and the pinch bolts correctly torqued, the hex-head screw is simply dead weight. It doesn't actually help 'hold' the axle in place - that's what the pinch bolts are for.
Want to get rid of 50g of unsprung weight? Torque your pinch bolts, and leave the hex-head screw in your toolbox.
