Illuminated reticles, if very good ones, can provide a much enhanced "cross hair" view, especially when the background is confused gray or black. Most people that "hunt" or shoot after sundown will admit that fine duplex reticles can almost be lost in the background maze. If you cannot distinguish your aiming point, it may be difficult for you to place it over your intended point of impact.
Most hunting scopes of quality such as Leupold use only a tiny + in the center of the duplex reticle and then they provide 11 levels of illumination. Burris provides a single dot at the POA and multiple levels of illumination. If you have the illumination set too high it will provide a halo effect and the light can actually block vision of the target by a form of halo glare. The lowest level of illumination should be used at all times to avoid this.
A very illustrative advantage of an illuminated reticle militarily would be something like this. On a total black night with no moon and few stars, a target at some distance is enjoying a cigarette. You know this because the bright, varying to dim, red coal out there is not all that difficult to see. The cigarettes operator can probably even be viewed in quality optics due to the glow reflecting off of the features. Problem is, that with no external natural illumination and no IR or thermal sighting equipment your reticle is not visable for aiming. A nice level two or three on illuminated reticle and the little red + goes to one side of the little red coal and the target is neutralized. Hopefully, no one viewed the momentary presence of your rifles muzzle blast.
Disadvantages of the illuminated reticles hover around the battery. Batteries tend to become disfunctional at very cold temperatures and their performance can be inadequate. The batteries are usually located under a cover on the illumination level knob. If a second battery is carried in an inner pocket where body heat can maintain its warmth, it can be changed out with the operational battery as the time of need arrives.
If I had an option, I would choose the quality illuminated reticle. If you have never shot an illuminated before, so be it, leave it off and you will never miss it. On the other hand having it when you could really use it at least gives the opportunity to improve your aiming capability. Keeping the battery in operational condition would only be a minor line on a good shooters page of readiness.
Seeing is Believing