Ok a little clarification. the enable lines. that simply turns on/off an axis? is there any reason why these lines shouldn't just be tied directly to +5v?  why would you want to shut off 1 or all axis? without shutting off the whole controller?

No reason why you cant just take them all to +5 Volts.

There are some occasions when I wish to disable just one axis.

When working on long jobs (longer than the working table) I produce the artwork in one piece and with a pause in the GCode at the appropriate point I disable the Y axis, release the work (which remains in the same place) whilst the table is moved by hand to the new location. The work is re-clamped, the axis enabled and the job restarted. I have tried various other methods and this system works best for me when making long signs.

When I use the laser head, the Z axis carries the focus lens assembly and once set remains the same for the entire job. I use standard engraving GCode and therefore any Z commands will alter the focus so disabling just the Z axis prevents this.

There are other occasions but it is one of those things that once you have it then you find the uses for it.  

Tweakie.