I personally used to hate having to constantly add or subtract the declination amount to convert grid to magnetic and magnetic to grid.  When I was a map reading instructor in the Army, one of the most common mistakes I saw was people messing up on the conversion between grid north and magnetic north and magnetic north to grid north.  Having a declination adjustable compass means there is no conversion.  What you see on the compass is the same as on the map.  Effortless.
A declination adjustment is a handy thing to have, 
after you've learned the difference between grid and mag north.  
Also, the see-through civilian compasses can be used as a protractor as well as a compass, which is handy.  I've lost a lot of military protractors in my time!  
In a pinch, you can use the compass to physically orient the map and then get a bearing without using a protractor, but it is less than ideal.  
I originally kicked myself for opting for the non-tritium model, but now I've had it so long that the tritium would be about worn out anyway.  Mine has a glow in the dark source that you "charge" with a flashlight.  It then proceeds to glow so bright it ruins your night vision until shortly before it glows too dim to read.