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Hi David,
As has been stated above.
In addition, some people also use them for visual observing to "perfectly" center their target when they align their Digital Setting Circles and Digital Telescope Computers like the Argo Navis. However, this IMO is not necessary for a high quality alignment for visual astronomy.
You can also take an illuminated reticle eyepiece to the next level, which is an astrometric eyepiece. This is an illuminated eyepiece with internal scales etched on glass for taking angular size measurements of astronomical features like double stars, moon craters and planetary features. You can also use them to measure the size of DSO's and their features.
Cheers,
John B
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