I never did one, but I can't say that I'm sorry for that. Some think that a residency might be for students that do not feel comfortable in their clinical or decision making skills (only applies to some). Some want a residency to enhance skills in a certain area, or to see patients mostly on their own but still have another doctor to talk with about a case. Some want the ability to teach academia, or work in a Veteran's hospital.
All residencies are not created equal, and I WOULD definitely stay away from school residencies. Every one i've witnessed are not very advantageous for a new clinician (just my opinion). A few Ophthalmologists like seeing an OD complete one if you're considering working for OMD (although not a requirement).
Personally, I just wanted to get out and start working. I had no desire to ever do Vision therapy, and contact lenses are not that hard to fit when you get out unless you're doing speciality RGP fits all the time. I completed four rotations of Ocular Disease because it interested me the most. I think a disease residency would be the most beneficial (again just my opinion).
Hope you find the answer to your question. Make sure you mesh with the attending doctor at the residency, you're with them for a full year. My friend from OD school hates his attending, and can't wait til June when his residency ends.