It is very much worth it, but don't spring for a cheap coating either. The Factory coats (These are pre-coated cheap lenses) will usually peel or start breaking down within 8 months to 1.5 years.
A good coating (The best brand names are Zeiss Teflon or Crizal Alize) will last at least 2 or more years and will be both Hydrophobic (repels liquids) and scratch resistant via a top surface hardcoat.
My personal choice is the Zeiss Teflon coating, it is what I use. The microfiber cloths will not actually fill in scratches I'm afraid, but they will do a better job of cleaning the lenses. The most important thing to remember is if you can always rinse off or wet the lenses before cleaning them... yes even with the micro fiber cloths.
What happens is that we walk around getting dust, dirt and pollutions on our lenses, then we take a dry cloth and rub it all in... this does not usually show up right away, but builds up over time into a sort of foggy looking film of scratches.
A good coating will really help relieve eyestrain from the computer and will crisp up your vision from any artificially reflected light source.... like a computer.
For example... you are driving at night and a headlight is coming towards you and you see a halo around the light. The halo is not from the light itself, but the light bouncing off the front and back surface of the lens as glare. Remove the glare and remove the halo's, which results in crisper sharper vision.
Another side effect of course is that people can see your eyes more clearly... better for business and better for all the attractive women looking at your face
Lastly it is great for photo's since you will see hardly any of the flash or other images reflected in the glasses.
A good coating is around 98% reflection free, and an all around good idea
Polarized lenses are predominantly used for sunglasses and are better for day time use. Polarized lenses block out horizontal glare, so are great for fishing or water sports/activities. A good test to see if your sunglasses are polarized is to put 2 pairs of polarized glasses back to back then rotate one pair of the glasses 90 degrees. If they are polarized looking though both pairs will turn the lenses opaque. This is because one pair is at a horizontal angle and will be blocking glare horizontally, and the rotated pair will now be blocking vertical glare... thereby making the 2 pairs together opaque to look through.
I have polarized lenses with a back surface Anti-Reflective coating, (in prescription) this is about the best pair of sunglasses you can put together in terms of glare and protection. If you look a t a good pair of lenses from a company such as Revo or Maui Jim, you will notice that as well as being polarized they also have the backside Anti-Reflective coating too.
Typically with dark lenses, since you are blocking transmittable light, you are likely to have more light reflect off of the surfaces. With sunglasses this is not so important for the front of the lenses as you will not see halos like artificial nighttime lighting, but often people will see reflections of things like their eyes and/or surrounding objects reflected in the back side of the lenses.
